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Costas Vassilakis - Scientific publications
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2020

  1. [c128]
    Mathas, C-M.; Grammatikakis, K-P.; Vassilakis, C.; Kolokotronis, N.; Bilali, V-G. and Kavallieros, D. Threat landscape for smart grid systems. In Proceedings of the 15th International Conference on Availability, Reliability and Security, ACM, 2020.Abstract & details DOI: https://doi.org/10.1145/3407023.3409229 BibTeX
    Abstract
    Smart Grids are energy delivery networks, constituting an evolution of power grids, in which a bidirectional flow between power providers and consumers is established. These flows support the transfer of electricity and information, in order to support automation actions in the context of the energy delivery network. Insofar, many smart grid implementations and implementation proposals have emerged, with varying degrees of feature delivery and sophistication. While smart grids offer many advantages, their distributed nature and information flow streams between energy producers and consumers enable the launching of a number of attacks against the smart grid infrastructure, where the related consequences may range from economic loss to complete failure of the smart grid. In this paper, we survey the threat landscape of smart grids, identifying threats that are specific to this infrastructure, providing an assessment of the severity of the consequences of each attack type, discerning features that can be utilized to detect attacks and listing methods that can be used to mitigate them.
    Keywords
    Smart grids, security, attacks, attack detection features, attack mitigation
  2. [j73]
    Spiliotopoulos, D.; Margaris, D. and Vassilakis, C. Data-Assisted Persona Construction Using Social Media Data. In Big Data and Cognitive Computing, 4 (3): 21, 2020.Abstract & details DOI: 10.3390/bdcc4030021 BibTeX
    Abstract
    User experience design and subsequent usability evaluation can benefit from knowledge about user interaction, types, deployment settings and situations. Most of the time, the user type and generic requirements are given or can be obtained and used to model interaction during the design phase. The deployment settings and situations can be collected through the needfinding phase, either via user feedback or via the automatic analysis of existing data. Personas may be defined using the aforementioned information through user research analysis or data analysis. This work utilizes an approach to activate an accurate persona definition early in the design cycle, using topic detection to semantically enrich the data that are used to derive the persona details. This work uses Twitter data from a music event to extract information that can be used to assist persona creation. A user study in persona construction compares the topic modelling metadata to a traditional user collected data analysis for persona construction. The results show that the topic information-driven constructed personas are perceived as having better clarity, completeness and credibility. Additionally, the human users feel more attracted and similar to such personas. This work may be used to model personas and recommend suitable ones to designers of other products, such as advertisers, game designers and moviegoers.
    Keywords
    persona; user experience; user interface design; topic modelling; usability; personalization; cultural events
  3. [j72]
    Spiliotopoulos, D.; Makri, E.; Vassilakis, C. and Margaris, D. Multimodal Interaction: Correlates of Learners' Metacognitive Skill Training Negotiation Experience. In Information, 11 (8): 381, 2020.Abstract & details DOI: 10.3390/info11080381 BibTeX
    Abstract
    Metacognitive training reflects knowledge, consideration and control over decision-making and task performance evident in any social and learning context. Interest in understanding the best account of effective (win-win) negotiation emerges in different social and cultural interactions worldwide. The research presented in this paper explores an extended study of metacognitive training system during negotiation using an embodied conversational agent. It elaborates on the findings from the usability evaluation employing 40 adult learners pre- and postinteraction with the system, reporting on the usability and metacognitive, individual- and community-level related attributes. Empirical evidence indicates (a) higher levels of self-efficacy, individual readiness to change and civic action after user-system experience, (b) significant and positive direct associations between self-efficacy, self-regulation, interpersonal and problem-solving skills, individual readiness to change, mastery goal orientation and civic action pre- and postinteraction and (c) gender differences in the perceptions of system usability performance according to country of origin. Theoretical and practical implications in tandem with future research avenues are discussed in light of embodied conversational agent metacognitive training in negotiation.
    Keywords
    Persona; User Experience; User Interface Design; Topic Modelling; Usability, Big Data; Personalization; Cultural Events
  4. [j71]
    Margaris, D.; Spiliotopoulos, D.; Karagiorgos, G. and Vassilakis, C. An Algorithm for Density Enrichment of Sparse Collaborative Filtering Datasets Using Robust Predictions as Derived Ratings. In Algorithms, 13 (7): 174, 2020.Abstract & details DOI: https://doi.org/10.3390/a13070174 BibTeX
    Abstract
    Collaborative filtering algorithms formulate personalized recommendations for a user, first by analysing already entered ratings to identify other users with similar tastes to the user (termed as near neighbours), and then using the opinions of the near neighbours to predict which items the target user would like. However, in sparse datasets, too few near neighbours can be identified, resulting in low accuracy predictions and even a total inability to formulate personalized predictions. This paper addresses the sparsity problem by presenting an algorithm that uses robust predictions, that is predictions deemed as highly probable to be accurate, as derived ratings. Thus, the density of sparse datasets increases, and improved rating prediction coverage and accuracy are achieved. The proposed algorithm, termed as CFDR, is extensively evaluated using (1) seven widely-used collaborative filtering datasets, (2) the two most widely-used correlation metrics in collaborative filtering research, namely the Pearson correlation coefficient and the cosine similarity, and (3) the two most widely-used error metrics in collaborative filtering, namely the mean absolute error and the root mean square error. The evaluation results show that, by successfully increasing the density of the datasets, the capacity of collaborative filtering systems to formulate personalized and accurate recommendations is considerably improved.
    Keywords
    recommender systems; collaborative filtering; sparse datasets; density enrichment; robust predictions; derived ratings; rating prediction coverage; rating prediction accuracy
  5. [j70]
    Margaris, D.; Vassilakis, C. and Spiliotopoulos, D. What makes a review a reliable rating in recommender systems?. In Information Processing & Management, 57 (6): 102304, 2020.Abstract & details DOI: https://doi.org/10.1016/j.ipm.2020.102304 BibTeX
    Abstract
    The way that users provide feedback on items regarding their satisfaction varies among systems: in some systems, only explicit ratings can be entered; in other systems textual reviews are accepted; and in some systems, both feedback types are accommodated. Recommender systems can readily exploit explicit ratings in the rating prediction and recommendation formulation process, however textual reviews -which in the context of many social networks are in abundance and significantly outnumber numeric ratings- need to be converted to numeric ratings. While numerous approaches exist that calculate a user's rating based on the respective textual review, all such approaches may introduce errors, in the sense that the process of rating calculation based on textual reviews involves an uncertainty level, due to the characteristics of the human language, and therefore the calculated ratings may not accurately reflect the actual ratings that the corresponding user would enter. In this work (1) we examine the features of textual reviews, which affect the reliability of the review-to-rating conversion procedure, (2) we compute a confidence level for each rating, which reflects the uncertainty level for each conversion process, (3) we exploit this metric both in the users’ similarity computation and in the prediction formulation phases in recommender systems, by presenting a novel rating prediction algorithm and (4) we validate the accuracy of the presented algorithm in terms of (i) rating prediction accuracy, using widely-used recommender systems datasets and (ii) recommendations generated for social network user satisfaction and precision, where textual reviews are abundant.
    Keywords
    Recommender systems, Collaborative filtering ,Rating prediction using textual information, Confidence level, Feature selection
  6. [bc11]
    Mathas, C-M. and Vassilakis, C. Reconnaissance. In Cyber-Security Threats, Actors, and Dynamic Mitigation, CRC Press, 2020.To appearAbstract & details BibTeX
    Abstract
    Reconnaissance is the phase of gathering information about an organization’s network and computing devices. This information includes both technical characteristics, such as IP addresses and software, and non-technical aspects, such as people operating the devices and the business value of tangible or intangible assets associated with the computing infrastructure. This information allows attackers to better understand their target and prepare elaborate attack plans. The reconnaissance phase is itself divided in a number of subphases, and each subphase is supported by a multitude of tools. In this chapter, we firstly describe in more detail the reconnaissance phase, while subsequently we present the different subphases and the methods and tools supporting each one, providing specific examples of how reconnaissance actions are performed. The information presented in this chapter can be used by organizations’ cyber-security officers to identify weaknesses in the organizations’ security plan implementations and take appropriate mitigation measures.
    Keywords
    Reconnaissance, Cyber-Security Threats, Actors, Dynamic Mitigation
  7. [j69]
    Deligiannis, K.; Raftopoulou, P.; Tryfonopoulos, C.; Platis, N. and Vassilakis, C. Hydria: An Online Data Lake for Multi-Faceted Analytics in the Cultural Heritage Domain. In Big Data and Cognitive Computing, 4 (2): 7, 2020.Abstract & details Full text DOI: 10.3390/bdcc4020007 BibTeX
    Abstract
    Advancements in cultural informatics have significantly influenced the way we perceive, analyze, communicate and understand culture. New data sources, such as social media, digitized cultural content, and Internet of Things (IoT) devices, have allowed us to enrich and customize the cultural experience, but at the same time have created an avalanche of new data that needs to be stored and appropriately managed in order to be of value. Although data management plays a central role in driving forward the cultural heritage domain, the solutions applied so far are fragmented, physically distributed, require specialized IT knowledge to deploy, and entail significant IT experience to operate even for trivial tasks. In this work, we present Hydria, an online data lake that allows users without any IT background to harvest, store, organize, analyze and share heterogeneous, multi-faceted cultural heritage data. Hydria provides a zero-administration, zero-cost, integrated framework that enables researchers, museum curators and other stakeholders within the cultural heritage domain to easily (i) deploy data acquisition services (like social media scrapers, focused web crawlers, dataset imports, questionnaire forms), (ii) design and manage versatile customizable data stores, (iii) share whole datasets or horizontal/vertical data shards with other stakeholders, (iv) search, filter and analyze data via an expressive yet simple-to-use graphical query engine and visualization tools, and (v) perform user management and access control operations on the stored data. To the best of our knowledge, this is the first solution in the literature that focuses on collecting, managing, analyzing, and sharing diverse, multi-faceted data in the cultural heritage domain and targets users without an IT background.
    Keywords
    cultural heritage; big data management; data lake; data store; analytics and visualization; open source
  8. [j68]
    Vassilakis, C.; Kotis, K.; Spiliotopoulos, D.; Margaris, D.; Kasapakis, V.; Anagnostopoulos, C-N.; Santipantakis, G.; Vouros, G. A.; Kotsilieris, T.; Petukhova, V.; Malchanau, A.; Lykourentzou, I.; Helin, K. M.; Revenko, A.; Gligoric, N. and Pokric, B. A Semantic Mixed Reality Framework for Shared Cultural Experiences Ecosystems. In Big Data and Cognitive Computing, 4 (2): 6, 2020.Abstract & details DOI: https://doi.org/10.3390/bdcc4020006 BibTeX
    Abstract
    This paper presents SemMR, a semantic framework for modelling interactions between human and non-human entities and managing reusable and optimized cultural experiences, towards a shared cultural experience ecosystem that might seamlessly accommodate mixed reality experiences. The SemMR framework synthesizes and integrates interaction data into semantically rich reusable structures and facilitates the interaction between different types of entities in a symbiotic way, within a large, virtual, and fully experiential open world, promoting experience sharing at the user level, as well as data/application interoperability and low-effort implementation at the software engineering level. The proposed semantic framework introduces methods for low-effort implementation and the deployment of open and reusable cultural content, applications, and tools, around the concept of cultural experience as a semantic trajectory or simply, experience as a trajectory (eX-trajectory). The methods facilitate the collection and analysis of data regarding the behaviour of users and their interaction with other users and the environment, towards optimizing eX-trajectories via reconfiguration. The SemMR framework supports the synthesis, enhancement, and recommendation of highly complex reconfigurable eX-trajectories, while using semantically integrated disparate and heterogeneous related data. Overall, this work aims to semantically manage interactions and experiences through the eX-trajectory concept, towards delivering enriched cultural experiences.
    Keywords
    intelligent interaction; semantics; usability; mixed reality; cultural experience
  9. [j67]
    Margaris, D.; Kobusinska, A.; Spiliotopoulos, D. and Vassilakis, C. An Adaptive Social Network-Aware Collaborative Filtering Algorithm for Improved Rating Prediction Accuracy. In IEEE Access, 8: 68301-68310, 2020.Abstract & details DOI: 10.1109/access.2020.2981567 BibTeX
    Abstract
    When information from traditional recommender systems is augmented with information about user relationships that social networks store, more successful recommendations can be produced. However, this information regarding user relationships may not always be available, since some users may not consent to the use of their social network information for recommendations or may not have social network accounts at all. Moreover, the rating data (categories and characteristics of products) may be unavailable for a recommender system. In this paper, we present an algorithm that can be applied in any social network-aware recommender system that utilizes the users’ ratings on items and users’ social relations. The proposed algorithm addresses the issues of limited social network information or limited collaborative filtering information for some users by adapting its behavior, taking into account the density and utility of each user’s social network and collaborative filtering neighborhoods. Through this adaptation, the proposed algorithm achieves considerable improvement in rating prediction accuracy. Furthermore, the proposed algorithm can be easily implemented in recommender systems
    Keywords
    Social computing, recommender systems, performance evaluation
  10. [j66]
    Markri, E.; Spiliotopoulos, D.; Vassilakis, C. and Margaris, D. Human behaviour in multimodal interaction: main effects of civic action and interpersonal and problem-solving skills. In Journal of Ambient Intelligence and Humanized Computing, TBD (TBD): TBD, 2020.Abstract & details DOI: 10.1007/s12652-020-01846-x BibTeX
    Abstract
    Metacognitive skill training may rest within any kind of social interaction that requires awareness of what an individual and others think, in social, educational and organizational settings alike. This work explores an extensive study of multimodal application interaction (virtual agent, spoken dialogue, visual communication of progress) for metacognitive skill training via negotiation skill training settings. Human behaviour, as effected by civic action and interpersonal and problem-solving skill training, is investigated through interaction sessions with a virtual agent on multimodal multiparty negotiation. This work reports on the results of the user-system evaluation sessions involving 41 participants before-and-after interaction with the system, integrating macro- (dialogue system performance) and micro- (metacognitive-related and individual-and-community level-related attitudes and skills) factors. Findings indicate significant and positive relationships between user and system evaluation questions after interaction with the dialogue system and between self-efficacy, self-regulation, individual readiness to change, mastery goal orientation, interpersonal and problem-solving skills and civic action before-and-after the interaction experience. Implications, limitations and further research issues are discussed in light of context of the multimodal interaction and its effects on the human behaviour during metacognitive skill training.
    Keywords
    Multimodal Interaction; Human Behaviour; Skill Training; Metacognitive; Individual- and Community-Level Related Attitudes and Skills
  11. [j65]
    Aivazoglou, M.; Roussos, A.; Margaris, D.; Vassilakis, C.; Ioannidis, S.; Polakis, J. and Spiliotopoulos, D. A Fine-grained Social Network Recommender System. In Social Network Analysis and Mining, 10 (1), 2020.Abstract & details Full text DOI: 10.1007/s13278-019-0621-7 BibTeX
    Abstract
    Recommender systems have greatly evolved in recent years and have become an integral part of the Web. From e-commerce sites to mobile apps, our daily routine revolves around a series of “small” decisions that are influenced by such recommendations. In a similar manner, online social networks recommend only a subset of the massive amount of content published by a user’s friends. However, the prevalent approach for the content selection process in such systems is driven by the amount of interaction between the user and the friend who published the content. As a result, content of interest is often lost due to weak social ties. In this paper, we present a fine-grained recommender system for social ecosystems, designed to recommend media content (e.g., music videos, online clips) published by the user’s friends. The system design was driven by the findings of our qualitative user study that explored the value and requirements of a recommendation component within a social network. The core idea behind the proposed approach was to leverage the abundance of preexisting information in each user’s account for creating interest profiles, to calculate similarity scores at a fine-grained level for each friend. The intuition behind the proposed method was to find consistent ways to obtain information representations that can identify overlapping interests in very specific sub-categories (e.g., two users’ music preferences may only coincide on hard rock). While the system is intended as a component of the social networking service, we developed a proof-of-concept implementation for Facebook and explored the effectiveness of our underlying mechanisms for content analysis. Our experimental evaluation demonstrates the effectiveness of our approach, as the recommended content of interest was both overlooked by the existing Facebook engine and not contained in the users’ Facebook News Feed. We also conducted a user study for exploring the usability aspects of the prototype and found that it offers functionality that could significantly improve user experience in popular services.
    Keywords
    Social Networks, Recommender Systems, Content Analysis, Interest Profiles, Usability
  12. [c127]
    Koryzis, D.; Fitsilis, F.; Spiliotopoulos, D.; Theocharopoulos, T.; Margaris, D. and Vassilakis, C. Policy Making Analysis and Practitioner User Experience. In Proceedings of the 22nd International Conference on Human-Computer Interaction, Springer, 2020.Abstract & details BibTeX
    Abstract
    This article presents the work on social media analysis-driven policy-making platforms that are powered by classic social media analysis technologies, such as policy modelling, linguistic analysis, opinion mining, sentiment analysis and information visualization. The approach examines the user design perspective towards user experience in policymaking for all the innovative modules used. The technology behind such complex task is presented while the resulting platform is appraised on the potential for real world application. The findings drive the development and the requirements for the summative usability assessment tests. We also report on the level the practitioners adopted the policy formulation tools.
    Keywords
    policy making; social network analysis; opinion mining; content analysis; natural language interfaces; user experience
  13. [c126]
    Margaris, D.; Spiliotopoulos, D.; Vassilakis, C. and Karagiorgos, G. A User Interface for Personalized Web Service Selection in Business Processes. In Proceedings of the 22nd International Conference on Human-Computer Interaction, Springer, 2020.Abstract & details BibTeX
    Abstract
    Nowadays, due to the huge volume of information available on the web, the need for personalization is more than necessary. Choosing the right information for each user is as important as the way this information is presented to him or her. Currently, user-triggered recommendation requests for web services are implemented as an automatic recommendation based on parametric computation. This work reports on a specialized user interface for business processes, where writing code entails invocation of business process information. The paper presents the user interface design for Personalized Web Service Selection in Business Process scenario execution and the user evaluation by business process engineers.
    Keywords
    user interface, personalization, web services, adaptation, business processes, WS-BPEL
  14. [c125]
    Spiliotopoulos, D.; Poulopoulos, V.; Margaris, D.; Makri, E. and Vassilakis, C. MOOC Accessibility from the Educator Perspective. In Proceedings of the 22nd International Conference on Human-Computer Interaction, Springer, 2020.Abstract & details BibTeX
    Abstract
    This work presents the universal access design principles and methods for natural language communication design in e-learning for the disabled. It unfolds a theoretical perspective to the design-for-all methodology and provides a framework description for technologies for creating accessible content for educational content communication. Main concerns include the problem identification of design issues for universal accessibility of spoken material, the primary pedagogical aspects that such content implementation should follow upon, as well as look into the state of the most popular e-learning platforms for which educators create and communicate educational content in an e-learning environment. References to massive open online course platform types of content that exist at the moment are examined in order to understand the challenges of bridging the gap between the modern design of rich courses and universal accessibility. The paper looks into the existing technologies for accessibility and a frame for analysis, including methodological and design issues, available resources and implementation using the existing technologies for accessibility and the perception of the designer as well as the user standpoint. Finally, a study to inform and access how potential educators may perceive the accessibility factor shows that accessible content is a major requirement toward a successful path to universally accessible e-learning.
    Keywords
    MOOC, universal accessibility, design-for-all, speech processing, interactive e-learning, technologies for accessibility
  15. [c124]
    Spiliotopoulos, D.; Kotis, K.; Vassilakis, C. and Margaris, D. Semantics-Driven Conversational Interfaces for Museum Chatbots. In Proceedings of the 22nd International Conference on Human-Computer Interaction, volume "Culture and Computing", pages 255-266, Springer International Publishing, 2020.Abstract & details DOI: 10.1007/978-3-030-50267-6_20 BibTeX
    Abstract
    This work addresses the challenges of creating usable and personalized conversational interfaces for broad, yet applicable, domains that require user engagement and learning, such as museum chatbots. Whether the chatbots are standalone or coupled with virtual agents or real-life robots, the functional requirements for interaction that targets specific learning aspects would be expected to be more or less similar. This work reports on experimental semantics-driven conversational interface design for chatbots in museum settings, targeting visitors to converse about exhibits and learn information about their style, the artists, the era, and other aspects related to them. Depending on the semantics (presentation, learning, exploration), chatbot scenarios were designed and evaluated by participants in a formative evaluation. The evaluation show that user requirement perception manifests in expectations on the semantic level, instead of just the technical level. The results between the scenarios are compared to see how the semantics considered for the design transferred to the implementation and to the user perception.
    Keywords
    semantics, conversational interfaces, chatbots, cultural technology
  16. [c123]
    Varitimiadis, S.; Kotis, K.; Spiliotopoulos, D.; Vassilakis, C. and Margaris, D. “Talking” Triples to Museum Chatbots. In Proceedings of the 22nd International Conference on Human-Computer Interaction, volume "Culture and Computing", pages 281-299, Springer International Publishing, 2020.Abstract & details DOI: 10.1007/978-3-030-50267-6_22 BibTeX
    Abstract
    The paper presents recent work on the design and development of AI chatbots for museums using Knowledge Graphs (KGs). The utilization of KGs as a key technology for implementing chatbots raises not only issues related to the representation and structuring of exhibits’ knowledge in suitable formalism and models, but also issues related to the translation of natural language dialogues to and from the selected technology for the formal representation and structuring of information and knowledge. Moreover, such a translation must be as transparent as possible to visitors, towards a realistic human-like question-answering process. The paper reviews and evaluates a number of recent approaches for the use of KGs in developing AI chatbots, as well as key tools that provide solutions for natural language translation and the querying of Knowledge Bases and Linked Open Data sources. This evaluation aims to provide answers to issues that are identified within the proposed MuBot approach for designing and implementing AI chatbots for museums. The paper also presents Cretan MuBot, the first experimental KG/Ontology-based AI chatbot of the MuBot Platform, which is under development in the Heracleum Archaeological Museum.
    Keywords
    knowledge graphs, RDF triples, NLP, chatbots, museums
  17. [j64]
    Sotiropoulos, P. and Vassilakis, C. Detection of intermittent faults in software programs through identification of suspicious shared variable access patterns. In Journal of Systems and Software, 159: 110455, 2020.Abstract & details Full text DOI: 10.1016/j.jss.2019.110455 BibTeX
    Abstract
    Intermittent faults are a very common problem in the software world, while difficult to be debugged. Most of the existing approaches though assume that suitable instrumentation has been provided in the program, typically in the form of assertions that dictate which program states are considered to be erroneous. In this paper we propose a method that can be used to detect probable sources of intermittent faults within a program. Our method proposes certain points in the code, whose data interdependencies combined with their execution interweaving indicate that they could be the cause of intermittent faults. It is the responsibility of the user to accept or reject these proposals. An advantage of this method is that it removes the need for having predefined assertion points in the code, being able to detect potential sources of intermittent faults in the whole bulk of the code, with no instrumentation requirements on the side of the programmer. The proposed approach exploits information from the dynamic behavior of the program. In comparison with parser-based approaches which analyze only the program structure, our approach is immutable to language term changes and in general is not depending on any user-provided assertions or configuration.
    Keywords
    Intermittent faults; Fault detection; Shared variables; Model-based checking
  18. [c122]
    Lykourentzou, I.; Liapis, A.; Papastathis, C.; Papangelis, K. and Vassilakis, C. Exploring Self-organisation in Crowd Teams. In IFIP Advances in Information and Communication Technology, pages 164-175, Springer International Publishing, 2020.Abstract & details DOI: 10.1007/978-3-030-39634-3_15 BibTeX
    Abstract
    Online crowds have the potential to do more complex work in teams, rather than as individuals. Team formation algorithms typically maximize some notion of global utility of team output by allocating people to teams or tasks. However, decisions made by these algorithms do not consider the decisions or preferences of the people themselves. This paper explores a complementary strategy, which relies on the crowd itself to self-organize into eective teams. Our preliminary results show that users perceive the ability to choose their teammate extremely useful in a crowdsourcing setting. We also nd that self-organisation makes users feel more productive, creative and responsible for their work product.
    Keywords
    crowd teams, self-organization, computer-supported collaboration, creative writing
  19. [c121]
    Theodoropoulos, A.; Vassilakis, C.; Antoniou, A.; Wallace, M. and Lepouras, G. ATMF: A Student-Centered Framework for the Effective Implementation of Alternative Teaching Methods for CSEd. In IFIP Advances in Information and Communication Technology, pages 116-127, Springer International Publishing, 2020.Abstract & details DOI: 10.1007/978-3-030-39634-3_11 BibTeX
    Abstract
    The dynamic development of Informatics introduces new educational and pedagogical challenges, including the instructional design of teaching and learning. How can we teach our students better in such a growing and demanding field? Moreover, how can we motivate them and together have better learning results? This paper aims to give answers to these questions, through a student-centered framework for effectively encompassing alternative teaching methods within CS. The proposed framework (ATMF) summarizes the benefits of alternative teaching methods in contrast with known is-sues of traditional teaching. In addition, ATMF is built upon empirical evidence and concludes that alternative practices, if used under the right conditions, can provide increased motivation for learning and better learning outcomes.
    Keywords
    Computer Science Education, Teaching Framework, Alternative Teaching Methods
  20. [j63]
    Margaris, D. and Vassilakis, C. Improving collaborative filtering’s rating prediction coverage in sparse datasets by exploiting the ’friend of a friend’ concept. In International Journal of Big Data Intelligence, 7 (1): 47-57, 2020.Abstract & details DOI: 10.1504/ijbdi.2020.106178 BibTeX
    Abstract
    Collaborative filtering computes personalized recommendations by taking into account ratings expressed by users. Collaborative filtering algorithms firstly identify people having similar tastes, by examining the likeness of already entered ratings. Users with highly similar tastes are termed “near neighbours” and recommendations for a user are based on her near neighbours’ ratings. However, for a number of users no near neighbours can be found, a problem termed as the “gray sheep” problem. This problem is more intense in sparse datasets, i.e. datasets with relatively small number of ratings, compared to the number of users and items. In this work, we propose an algorithm for alleviating this problem by exploiting the friend of a friend (FOAF) concept. The proposed algorithm, CFfoaf, has been evaluated against eight widely used sparse datasets and under two widely used collaborative filtering correlation metrics, namely the Pearson Correlation Coefficient and the Cosine Similarity and has been proven to be particularly effective in increasing the percentage of users for which personalized recommendations can be formulated in the context of sparse datasets, while at the same time improving rating prediction quality.
    Keywords
    collaborative filtering, recommender systems, sparse datasets, friend-of-a-friend, Pearson correlation coefficient, cosine similarity, evaluation, prediction accuracy
  21. [j62]
    Margaris, D. and Vassilakis, C. Improving collaborative filtering’s rating prediction accuracy by considering users’ dynamic rating variability. In International Journal of Big Data Intelligence, 7 (2): 59-71, 2020.Abstract & details DOI: 10.1504/ijbdi.2020.107373 BibTeX
    Abstract
    Users that populate ratings databases, follow different marking practices, in the sense that some are stricter, while others are more lenient. Similarly, users’ rating practices may also differ in rating variability, in the sense that some users may be entering ratings close to their mean, while other users may be entering more extreme ratings, close to the limits of the rating scale. While this aspect has been recently addressed through the computation and exploitation of an overall rating variability measure per user, the fact that user rating practices may vary along the user’s rating history time axis may render the use of the overall rating variability measure inappropriate for performing the rating prediction adjustment. In this work, we (1) propose an algorithm that considers two variability metrics per user, the global (overall) and the local one, with the latter representing the user’s variability at prediction time, (2) present alternative methods for computing a user’s local variability and (3) evaluate the performance of the proposed algorithm in terms of rating prediction quality and compare it against the state-of-the-art algorithm that employs a single variability metric in the rating prediction computation process.
    Keywords
    collaborative filtering, users’ ratings dynamic variability, Pearson correlation coefficient, cosine similarity, evaluation, prediction accuracy

2019

  1. [c120]
    Wallace, M.; Poulopoulos, V.; Antoniou, A.; Vassilakis, C.; Lepouras, G.; Diakoumakos, J. and Panagiotidou, V. Kalamata 1821: Roads of Freedom - Digital applications teach history (Greek title: Καλαμάτα 1821: Δρόμοι Ελευθερίας – Οι ψηφιακές εφαρμογές διδάσκουν ιστορία). In 2nd Panhellenic conference on Open Educational Resources and e-learning, 2019.(Original paper in Greek)Abstract & details BibTeX
    Abstract
    The “Kalamata 1821: Roads of Freedom” project is an effort for scientifically organizing the celebration of the 200-year anniversary from the liberation of Greece from the Turkish thrall, with a special focus on the city of Kalamata. The project, aiming to link historical memories to the modern era, includes a major section related to the development of digital applications. The project’s digital applications are developed by the Knowledge and Uncertainty lab of the Department of Informatics and Telecommunications of the University of the Peloponnese. The digital applications are based on the information provided by the historical scientific team of the project. Within the project, two distinct groups of applications are developed, in order to cover the diverse needs of the target population. The nature of the applications is clearly didactic, offering detailed information regarding historical facts, places and persons which relate to the Greek War of Independence, as well as on locations where important events took place. The Interactive Table applications are a group of applications which will be available to the public visiting the historic building of the old Town Hall of Kalamata, where the project exhibition center is located. These applications constitute a modern, interactive, digital encyclopedia of the relation between the city of Kalamata and the Greek War of Independence. For the Interactive Table, three original applications were developed. The first depicts histories and facts linked to some points on a map. The second presents a tree of histories, that is histories that are interrelated, and where each visitor may familiarize with facts and persons that are linked to each other. Finally, the third application focuses on images and multimedia, challenging the visitors to identify and elaborate on events and histories hiding behind pictures. The second group consists of a single application that targets on a wider public that prefers a different type on interaction. Effectively this application implements a scavenger hunt with historic content. The goal of this application is to motivate the visitor of the city of Kalamata to wander around the city, and also to link the project to the local market.
    Keywords
    Interactive table; Educational applications; Mobile applications
  2. [j61]
    Margaris, D.; Vassilakis, C. and Spiliotopoulos, D. Handling uncertainty in social media textual information for improving venue recommendation formulation quality in social networks. In Social Network Analysis and Mining, 9 (1): 19, 2019.Abstract & details Full text DOI: 10.1007/s13278-019-0610-x BibTeX
    Abstract
    One of the major problems that social media front is to continuously produce successful, user-targeted information, in the form of recommendations, which are produced by applying methods from the area of recommender systems. One of the most important applications of recommender systems in social networks is venue recommendation, targeted by the majority of the leading social networks (Facebook, TripAdvisor, OpenTable, etc.). However, recommender systems' algorithms rely only on the existence of numeric ratings which are typically entered by users, and in the context of social networks, this information is scarce, since many social networks allow only reviews, rather than explicit ratings. Even if explicit ratings are supported, users may still resort to expressing their views and rating their experiences through submitting posts, which is the predominant user practice in social networks, rather than entering explicit ratings. User posts contain textual information, which can be exploited to compute derived ratings, and these derived ratings can be used in the recommendation process in the lack of explicitly entered ratings. Emerging recommender systems encompass this approach, without however tackling the fact that the ratings computed on the basis of textual information may be inaccurate, due to the very nature of the computation process. In this paper, we present an approach which extracts features of the textual information, a widely available source of information in venue category, to compute a confidence metric for the ratings that are computed from texts; then, this confidence metric is used in the user similarity computation and venue rating prediction formulation process, along with the computed rating. Furthermore, we propose a venue recommendation method that considers the generated venue rating predictions, along with venue QoS, similarity and spatial distance metrics in order to generate venue recommendations for social network users. Finally, we validate the accuracy of the rating prediction method and the user satisfaction from the recommendations generated by the recommendation formulation algorithm. Conclusively, the introduction of the confidence level significantly improves rating prediction accuracy, leverages the ability to generate personalized recommendations for users and increases user satisfaction.
    Keywords
    Social networks; Recommender systems; Collaborative filtering; Venue recommendation formulation; Rating prediction; Textual information; Uncertainty; Confidence level
  3. [c119]
    Wallace, M.; Poulopoulos, V.; Lepouras, G.; Vassilakis, C. and Antoniou, A. Scavenger Hunt in the Roads of Freedom (Greek title: “Κυνήγι θησαυρού στους Δρόμους της Ελευθερίας"). In Proceedings of the 3nd Pan-Hellenic Conference on Digital Cultural Heritage-EuroMed 2019, 2019.(Original paper in Greek)Abstract & details BibTeX
    Abstract
    The project "Kalamata 1821: Roads of freedom" is being funded in the context of the Action "RESEARCH - CREATE - INNOVATE. The project, which encompasses original historic research work in the University of the Peloponnese, is an effort to narrate a historic course of 200 years for the city of Kalamata, from the eruption of the Greek revolution until today, through a modern and fresh perspective. This paper will present one of the digital applications developed within the project, and more specifically the Scavenger Hunt that is being developed by the Knowledge and Uncertainty lab of the Department of Informatics and Telecommunications in Tripolis. The game is designed for mobile devices and its goal is to link the historic content of the project with the contemporary city and, in a gamified fashion, assist the user not only to familiarize with the history of the city but also to navigate in the city and connect with the local market. By searching through pictures of various locations of the city, the visitor is directed to the most outstanding locations of the war of independence, and learns about the contribution of the city of Kalamata in this turning point for the history of the Greek nation. At the same time, the visitor is rewarded by receiving offers for local stores.
    Keywords
    Scavenger Hunt, Roads of Freedom, Greek War of Independence, Kalamata
  4. [c118]
    Wallace, M.; Poulopoulos, V.; Lepouras, G.; Vassilakis, C. and Antoniou, A. Supporting small museums through social network semantic analysis (Greek title: Υποστήριξη μικρών μουσείων μέσω της σημασιολογικής ανάλυσης κοινωνικών δικτύων). In Proceedings of the 3nd Pan-Hellenic Conference on Digital Cultural Heritage-EuroMed 2019, 2019.(Original paper in Greek)Abstract & details BibTeX
    Abstract
    Greece has a significant historic, archaeological and cultural wealth, and a big number of museums and related venues. Some of them are big, both in size and resources -human as well as financial. Most venues however are small in size, are not connected with larger organizations, have constrained budgets and little or no permanent staff. In this paper, we focus on that particular category of museums. Many of these museums possess noteworthy collections, and it would be desirable if the general public could enjoy them. Unfortunately, in most cases, even the existence of the museums is not generally known, even to inhabitants of the cities at which the museums are located. The small number of visitors leads to confined revenues, and this in turn leads to a situation which is not financially viable. In order for a small museum to survive, its existence and value must be made known to the wide public. However, this is inhibited due to the lack of resources to finance advertising and the lack of specialized personnel. In this paper, we combine our experiences on small museums, which has been developed within the CrossCult H2020 project, with know-how on social network analysis which has been gained in the context of the PaloAnalytics national project, in order to offer viable solutions for promotion, which are tailored to the needs of small museums.
    Keywords
    Social Networks; small-sized museums; semantic analysis
  5. [c117]
    Vassilakis, C.; Poulopoulos, V.; Wallace, M.; Antoniou, A. and Lepouras, G. TripMentor: Challenges and prospects for culture and tourism in the Attica region (Greek title: “TripMentor: προκλήσεις και προοπτικές για τον πολιτισμό και τον τουρισμό στην περιφέρεια Αττικής“). In Proceedings of the 3nd Pan-Hellenic Conference on Digital Cultural Heritage-EuroMed 2019, 2019.(Original paper in Greek)Abstract & details BibTeX
    Abstract
    This paper presents the TripMentor project which is related to the tourism and civilization in the region of Attica. The main goal of the project is the presentation, in two languages, of the rich cultural content of the region to the tourists, through an Internet-based environment and through mobile applications. The goal of the project is to guide the visitors through many possible alternative routes, which include points of interest, as well as enterprises with tourism-related offers, while at the same time attempts to combine these routes with cultural points of interest. The project interrelates information, venues and visitor profiles with an automated way, striving to offer a unique personalized experience, tailored to the needs and preferences of each user. The project challenges are mainly technical, since through the project procedures (a) information regarding the points of interest should be gathered in an automated fashion (b) information about events related to points of interest must be taken into account and (v) data related to users, and especially the user profiles must be discovered and exploited so that the available information can be synthesized into a unique experience. In this context, we present the project application domain and the related challenges.
    Keywords
    tourism, culture, visitor profile, cultural information, geospatial data, social networks
  6. [j60]
    Antoniou, A.; Morillo, S. R.; Lepouras, G.; Diakoumakos, J.; Vassilakis, C.; Nores, M. L. and Jones, C. E. Bringing a peripheral, traditional venue to the digital era with targeted narratives. In Digital Applications in Archaeology and Cultural Heritage, 14: e00111, 2019.Abstract & details Full text DOI: 10.1016/j.daach.2019.e00111 BibTeX
    Abstract
    The current work presents a method of enhancing museum content with narratives targeting history reflection in a personalized manner, delivered by an especially designed mobile app. The mobile app is a part of a technology ecosystem that supports the visitor before, during and after her visit. Within the framework of the European H2020 CrossCult project, a method was designed, implemented and tested to enhance museum content with digital material, enriched narratives and means to actively engage visitors. In particular, the method was implemented and tested for the content of the Archaeological Museum of Tripolis (Greece) and specific content examples are presented here, together with data from visitor evaluation. The results showed that content was significantly and qualitatively enhanced and visitors recognized the potential of the app in triggering visitor curiosity, new forms of engagement, and the ability to reflect on the connections between historical and social phenomena.
    Keywords
    Narratives; Cultural heritage; Museum app; Reflection; Visitor experience
  7. [c116]
    Spiliotopoulos, D.; Margaris, D.; Vassilakis, C.; Petukhova, V. and Kotis, K. A Mixed-reality Interaction-driven Game-based Learning Framework. In Proceedings of the 11th International Conference on Management of Digital EcoSystems, ACM, 2019.Abstract & details DOI: 10.1145/3297662.3365802 BibTeX
    Abstract
    This work presents a platform for linked legislative data to engage citizens in transparent and effective democracies. With a focus on scaling up participatory approaches from local to national level, the approach extends well established and open source tools and technologies, to build mobile monitoring and analysis tools that increase transparency of law-making and implementation to citizens. This is achieved by combining open data and open services with user and citizen generated content, in order to address citizen’s needs in the context of open government. Data and feeds from trusted sources are interconnected with new and re-purposed data feeds generated by users via the social web to form a meaningful, searchable, customizable, re-usable and open data-focused personalised mobile public service approach. The framework exploits the social aspects of open data, as well as the training of users, citizens and public servants to be able to understand and demand useful public open data, as well as facilitate the opening of more data.
    Keywords
    Mobile Public Services; Natural Language Processing; Citizen Engagement; Policy Modelling; e-Government; Transparency; Accountability; Legislation
  8. [c115]
    Spiliotopoulos, D.; Margaris, D. and Vassilakis, C. Citizen Engagement for Transparent and Accountable Policy Modelling. In Proceedings of the 11th International Conference on Management of Digital EcoSystems, ACM, 2019.Abstract & details DOI: 10.1145/3297662.3365813 BibTeX
    Abstract
    In the modern information society, learning is no longer just about obtaining factual knowledge, but more about general skills on how and where to apply available knowledge and obtain new knowledge in order to solve new problems. Such skills include abilities to connect and organize ideas, fill gaps in knowledge structures, evaluate evidence, argue with new information, test and modify, predict, clarify, generate questions, learn new concepts, make unexpected connections, reflect, analyze, synthesize and loop back. This work presents the Immersion framework, a digital ecosystem for adaptive smart learning environments for interactive mixed reality driven methods to foster learners’ self-regulating skill development.
    Keywords
    Mobile Learning; Mixed Reality; Self-regulated Learning; Game-based Interaction; Technology Enhanced Learning; Learner Collaboration
  9. [c114]
    Margaris, D.; Spiliotopoulos, D. and Vassilakis, C. Improving Collaborative Filtering’s Rating Prediction Quality by Exploiting the Item Adoption Eagerness Information. In Proceedings of the IEEE/WIC/ACM International Conference on Web Intelligence, ACM, 2019.Abstract & details DOI: 10.1145/3350546.3352544 BibTeX
    Abstract
    Collaborative filtering computes personalized recommendations by taking into account ratings expressed by users. Collaborative filtering algorithms firstly identify people having similar tastes, who are termed as “near neighbors" and recommendations for a user, are based on his near neighbors’ ratings. On the other hand, people exhibit different levels of eagerness to adopt new products: according to this characteristic, there is a set of users, termed as “Early Adopters", who are prone to start using a product or technology as soon as it becomes available, in contrast to the majority of users, who prefer to start using items once they reach maturity; this important aspect of user behavior is not taken into account by existing algorithms. In this work, we (1) propose an algorithm that considers the eagerness shown by users to adopt products, aiming to improve rating prediction quality and (2) evaluate the proposed algorithm against seven widely used datasets.
    Keywords
    collaborative filtering, item adoption eagerness, rating prediction quality, evaluation, Pearson correlation coefficient, cosine similarity
  10. [j59]
    Vassilakis, C. and Margaris, D. Editorial for the Special Issue on “Modern Recommender Systems: Approaches, Challenges and Applications”. In Information, 10 (7): 230, 2019.Abstract & details Full text DOI: 10.3390/info10070230 BibTeX
    Abstract
    This Special Issue on “Modern Recommender Systems: Approaches, Challenges and Applications” aims to promote new theoretical models, approaches, algorithms and applications related to the area of recommender systems. The papers in this special issue address a broad spectrum of issues regarding recommender systems: novel algorithms to improve recommender system performance in terms of prediction accuracy, utility and efficiency are introduced, an application of recommender systems to a specific area is presented, and a framework for recommender system evaluation is detailed. Finally, a comprehensive review on the use of opinion mining in recommender systems is included.
    Keywords
    -
  11. [c113]
    Spiliotopoulos, D.; Vassilakis, C. and Margaris, D. Data-driven country safety monitoring terrorist attack prediction. In Proceedings of the 2019 IEEE/ACM International Conference on Advances in Social Networks Analysis and Mining, ACM, 2019.Abstract & details DOI: 10.1145/3341161.3343527 BibTeX
    Abstract
    Terrorism is a key risk for prospective visitors of tourist desti-nations. This work reports on the analysis of past terrorist at-tack data, focusing on tourist-related attacks and attack types in Mediterranean EU area and the development of algorithms to predict terrorist attack risk levels. Data on attacks in 10 coun-tries have been analyzed to quantify the threat level of tourism-related terrorism based on the data from 2000 to 2017 and for-mulate predictions for subsequent periods. Results show that predictions on potential target types can be derived with ade-quate accuracy. Such results are useful for initiating, shifting and validating active terrorism surveillance based on real pre-dicted attack and target types per country.
    Keywords
    Data Analysis, Terrorist Attacks, Safety Perception, Risk Calculation, Threat Ranking
  12. [c112]
    Margaris, D.; Spiliotopoulos, D. and Vassilakis, C. Social relations versus near neighbours. In Proceedings of the 2019 IEEE/ACM International Conference on Advances in Social Networks Analysis and Mining, ACM, 2019.Abstract & details DOI: 10.1145/3341161.3345620 BibTeX
    Abstract
    Online advertising benefits by recommender systems since the latter analyse reviews and rating of products, providing useful insight of the buyer perception of products and services. When traditional recommender system information is enriched with social network information, more successful recommendations are produced, since more users’ aspects are taken into consid-eration. However, social network information may be unavaila-ble since some users may not have social network accounts or may not consent to their use for recommendations, while rating data may be unavailable due to the cold start phenomenon. In this paper, we propose an algorithm that combines limited col-laborative filtering information, comprised only of users’ ratings on items, with limited social network information, com-prised only of users’ social relations, in order to improve (1) prediction accuracy and (2) prediction coverage in collaborative filtering recommender systems, at the same time. The proposed algorithm considerably improves rating prediction accuracy and coverage, while it can be easily integrated in recommender systems.
    Keywords
    Online Advertising, Social Networks, Collaborative Filtering, Limited Information, Near Neighbours, Pearson Correlation Coefficient, Evaluation
  13. [c111]
    Margaris, D.; Vasilopoulos, D.; Vassilakis, C. and Spiliotopoulos, D. Improving Collaborative Filtering’s Rating Prediction Accuracy by Introducing the Common Item Rating Past Criterion. In Proceedings of the 10th International Conference on Information, Intelligence, Systems and Applications (IISA2019), IEEE, 2019.Best paper awardAbstract & details Full text DOI: 10.1109/IISA.2019.8900758 BibTeX
    Abstract
    Collaborative filtering computes personalized recommendations by taking into account ratings expressed by users. Collaborative filtering algorithms firstly identify people having similar tastes, by examining the likeness of already entered ratings. Users with highly similar tastes are termed “near neighbors” and recommendations for a user are based on his near neighbors’ ratings. In order to measure similarity between users, so as to determine a user’s NNs, a similarity metric is used. Insofar, similarity metrics proposed in the literature either consider all user ratings equally or take into account temporal variations within the users’ or items’ ratings history. However users’ ratings are co-shaped according to the experiences that they had in the past; therefore if two users enter similar (or dissimilar) ratings for an item while having experienced –to a large extent the same items in the past, this constitutes stronger evidence about user similarity (or dissimilarity). Insofar however, no similarity metric takes into account this aspect. In this work, we (1) propose an algorithm that considers the common item rating past in the rating prediction computation process, aiming to improve rating prediction quality, and (2) evaluate the proposed algorithm against seven widely used datasets, both dense and sparse, and considering two widely used user similarity metrics.
    Keywords
    Collaborative Filtering, Items’ Rating Sequence, Common Item Rating Past Criterion, Pearson Correlation Coeffi-cient, Cosine Similarity, Evaluation
  14. [c110]
    Margaris, D.; Vasilopoulos, D.; Vassilakis, C. and Spiliotopoulos, D. Improving Collaborative Filtering's Rating Prediction Coverage in Sparse Datasets through the Introduction of Virtual Near Neighbors. In 2019 10th International Conference on Information, Intelligence, Systems and Applications (IISA), IEEE, 2019.Abstract & details Full text DOI: 10.1109/iisa.2019.8900678 BibTeX
    Abstract
    Collaborative filtering creates personalized recommendations by considering ratings entered by users. Collaborative filtering algorithms initially detect users whose likings are alike, by ex-ploring the similarity between ratings that have insofar been submitted. Users having a high degree of similarity regarding their ratings are termed near neighbors, and in order to formu-late a recommendation for a user, her near neighbors’ ratings are extracted and form the basis for the recommendation. Col-laborative filtering algorithms however exhibit the problem commonly referred to as “gray sheep”: this pertains to the case where for some users no near neighbors can be identified, and hence no personalized recommendations can be computed. The “gray sheep” problem is more severe in sparse datasets, i.e. datasets where the number of ratings is small, compared to the number of items and users. In this paper, we address the “gray sheep” problem by introducing the concept of virtual near neighbors and a related algorithm for their creation on the basis of the existing ones. We evaluate the proposed algorithm, which is termed as CFVNN, using eight widely used datasets and consid-ering two correlation metrics which are widely used in Collabo-rative Filtering research, namely the Pearson Correlation Coef-ficient and the Cosine Similarity. The results show that the pro-posed algorithm considerably leverages the capability of a Col-laborative Filtering system to compute personalized recommen-dations in the context of sparse datasets, tackling thus efficiently the “gray sheep” problem. In parallel, the CFVNN algorithm achieves improvements in rating prediction quality, as this is expressed through the Mean Absolute Error and the Root Mean Square Error metrics.
    Keywords
    Collaborative Filtering, Sparse Datasets, Virtual Near Neighbors, Pearson Correlation Coefficient, Cosine Similarity, Evaluation
  15. [c109]
    Spiliotopoulos, D.; Vassilakis, C.; Margaris, D. and Kotis, K. A Methodology for Generated Text Annotation for High Quality Speech Synthesis. In 2019 10th International Conference on Information, Intelligence, Systems and Applications (IISA), IEEE, 2019.Abstract & details Full text DOI: 10.1109/iisa.2019.8900720 BibTeX
    Abstract
    Natural Language Generators may produce linguistically en-riched text descriptions that can lead to significantly improved quality of speech synthesis. There are cases, however, where either the generator modules produce pieces of non-analysed, non-annotated plain text, or such modules are not available at all. Moreover, the language analysis is restricted by the usually limited domain coverage of the generator. For those cases the enriched input to the speech synthesizer needs to be produced from plain text in order to maintain speech quality. This work reports on the method for automatic domain dependent annota-tion of plain text, through the utilisation of the linguistic infor-mation from rich generated text. The synthetic speech from the resulting prosody models is evaluated by human participants showing annotation results for plain text quite on par with the rich generated text. This leads to improved perceived natural-ness of the synthesized speech.
    Keywords
    Text-to-speech, Prosody enrichment, Natural language generation, Natural language processing, Semantic feature annotation
  16. [c108]
    Poulopoulos, V.; Wallace, M.; Vassilakis, C. and Lepouras, G. PaloAnalytics project concept, scope and outcomes: an opportunity for culture. In Proceedings of the Workshop on Cultural Informatics, co-located with the 14th International Workshop On Semantic And Social Media Adaptation And Personalization (SMAP 2019), 2019.Abstract & details Full text BibTeX
    Abstract
    This paper describes the national funded project entitled PaloAnalytics, which develops an innovative platform that allows companies and organizations, that operate in several countries, to monitor and analyze, in depth, the markets’ interest to their products and successfully plan their marketing and communication strategy, with data and insights collected from all the local media, and focuses on its application to cultural spaces and museums. In this notion, we examine the effect that this project can have in cultural spaces or companies related to arts and culture. PaloAnalytics platform allows organizations to investigate the impact of their products on consumers across different countries and this is achieved with the analysis of content from sites, blogs, social networks and open data. This implies that cultural organization can benefit by adopting the implemented services, so that the can recognize and analyze their audience, their online marketing campaigns as well as examine the impact of their messages and the spread of their messages on the Internet. In this paper, we briefly describe the project and discuss on the impact on cultural related organizations.
    Keywords
    big data, data monitoring, trending topics, influencers, infographics, data visualization, deep learning
  17. [c107]
    Vassilakis, C.; Poulopoulos, V.; Wallace, M.; Antoniou, A. and Lepouras, G. TripMentor Project: scope and challenges. In Proceedings of the Workshop on Cultural Informatics, co-located with the 14th International Workshop On Semantic And Social Media Adaptation And Personalization (SMAP 2019), 2019.Abstract & details Full text BibTeX
    Abstract
    We present Tripmentor, a novel project, that is related to tourism in the region of Attica. The project has as main scope to provide rich media content to tourists through a web and mobile environment in two languages trying to guide them through alternative routes that include places of interest as well as organizations with offers to tourists. The project interconnects people with places and events in an automated manner trying to personalize on each tourist’s personality. The challenges of the project are mainly technological as through the processes of the project a) automated information about venues must be collected, b) information about events related to venues must be fetched and finally c) data related to system users and mainly their profile should be discovered and created in order to offer a unique experience to each of them. We present the scope of the project as well as the challenges of its implementation.
    Keywords
    tripmentor, tourism, personalization, geodata, cultural related information, social media
  18. [c106]
    Kolokotronis, N.; Brotsis, S.; Germanos, G.; Vassilakis, C. and Shiaeles, S. On Blockchain Architectures for Trust-Based Collaborative Intrusion Detection. In 2019 IEEE World Congress on Services (SERVICES), IEEE, 2019.Abstract & details Full text DOI: 10.1109/services.2019.00019 BibTeX
    Abstract
    This paper considers the use of novel technologies for mitigating attacks that aim at compromising intrusion detection systems (IDSs). Solutions based on collaborative intrusion detection networks (CIDNs) could increase the resilience against such attacks as they allow IDS nodes to gain knowledge from each other by sharing information. However, despite the vast research in this area, trust management issues still pose significant challenges and recent works investigate whether these could be addressed by relying on blockchain and related distributed ledger technologies. Towards that direction, the paper proposes the use of a trust-based blockchain in CIDNs, referred to as trust-chain, to protect the integrity of the information shared among the CIDN peers, enhance their accountability, and secure their collaboration by thwarting insider attacks. A consensus protocol is proposed for CIDNs, which is a combination of a proof-of-stake and proof-of-work protocols, to enable collaborative IDS nodes to maintain a reliable and tampered-resistant trust-chain.
    Keywords
    Blockchain; security; collaborative intrusion detection; trust management; insider threats
  19. [c105]
    Antoniou, A.; Lepouras, G.; Vassilakis, C.; Wallace, M. and Platis, N. Cultural technologies: the case of the Tripolis archeological museum (Greek title: "ΠΟΛΙΤΙΣΤΙΚΕΣ ΤΕΧΝΟΛΟΓΙΕΣ: Η ΠΕΡΙΠΤΩΣΗ ΤΟΥ ΑΡΧΑΙΟΛΟΓΙΚΟΥ ΜΟΥΣΕΙΟΥ ΤΡΙΠΟΛΗΣ"). In Book of abstracts of the 2nd Conference of the School of Social Sciences of the University of the Aegean "Social sciences today: dilemmas and prospectives beyond the crisis", 2019.(Original paper in Greek)Abstract & details Full text BibTeX
    Abstract
    The Tripolis archeological museum hosts magnificent ancient art exhibits from the whole of the Arcadia county. However, a series of issues, including the old-style museological exhibition and the limited informational material offered to the visitor, combined with the lack of digital presence for the museum, lead to a low number of visitors. Culural technologies may offer solutions to these issues that the museum fronts, and to this end the museum was included in the CrossCult EU project (www.crosscult.eu). In the context of the project, the antecendents regarding the technological design for the particular museum were studied (staff, visitor and technological equipment needs), and the characteristics of the museum collections were examined. With the collaboration of the Ephorate of Antiquities of Arcadia, the most important and characteristic exhibits were identified, among those that were linked to the position of the woman in the ancient society. Using these exhibits as a basis, 7 thematic itineraries were created in both the English and the Greek language, which support the user in visiting the museum halls and exhibitions and learning certain aspects of women's lives in the antiquity (e.g. education, everyday life, social status, etc). Each exhibit is linked with different digital cultural artefacts (e.g. images from other collections, related videos, games, sound clips etc.), to create narratives that increase user engagement and stimulate reflection. In parallel, a series of games was deveped, aiming to disseminate the presence of the museum and the information sourced from it through the social networks, assist in creating user profiles and further promote the museum. Finally, user experience can continue after the visit, through the use of a specialized social network, created specifically for the needs of the museum. (Abstract in Greek follows: Το αρχαιολογικό μουσείο Τρίπολης στεγάζει καταπληκτικά δείγματα αρχαίας τέχνης από ολόκληρο τον νομό Αρκαδίας. Όμως μια σειρά προβλημάτων, όπως η παλαιού τύπου μουσειολογική έκθεση και το πολύ συνοπτικό πληροφοριακό υλικό που προσφέρεται στον επισκέπτη, μαζί με το γεγονός ότι το μουσείο δεν έχει ψηφιακή παρουσία, οδηγεί σε χαμηλή επισκεψιμότητα. Οι πολιτιστικές τεχνολογίες μπορούν να προσφέρουν λύσεις στα προβλήματα του μουσείου και έτσι το μουσείο εντάχθηκε στο Ευρωπαϊκό ερευνητικό έργο CrossCult (www.crosscult.eu). Μέσα στα πλαίσια του έργου, μελετήθηκαν τα προαπαιτούμενα σχεδιασμού τεχνολογιών για το συγκεκριμένο χώρο (ανάγκες προσωπικού, ανάγκες επισκεπτών, ανάγκες τεχνολογικού εξοπλισμού), καθώς και τα χαρακτηριστικά των συλλογών. Με τη βοήθεια της Εφορείας Αρχαιοτήτων Αρκαδίας, εντοπίστηκαν τα σημαντικότερα και χαρακτηριστικότερα εκθέματα, γύρω από το θέμα της θέσης της γυναίκας στον αρχαίο κόσμο. Με βάσει τα εκθέματα αυτά, δημιουργήθηκαν 7 θεματικές διαδρομές (σε Ελληνικά και Αγγλικά) όπου ο επισκέπτης μπορεί να περιηγηθεί στο μουσείο και να μάθει για συγκεκριμένες πτυχές της ζωής των γυναικών (π.χ. εκπαίδευση, καθημερινότητα, κοινωνική θέση, κλπ). Το κάθε έκθεμα συνδέεται με διαφορετικά ψηφιακά πολιτιστικά αντικείμενα (π.χ. εικόνες από εκθέματα άλλων συλλογών, σχετικά βίντεο, παιχνίδια, αρχεία ήχου, κλπ) για να δημιουργηθούν αφηγήσεις που να αυξάνουν τον προβληματισμό και την εμπλοκή του επισκέπτη. Παράλληλα, μια σειρά παιχνιδιών υλοποιήθηκε με σκοπό τη διάχυση στα μέσα κοινωνικής δικτύωσης για τη δημιουργία προφίλ επισκεπτών και την περαιτέρω διαφήμιση του μουσείου. Τέλος, η εμπειρία μπορεί να συνεχιστεί και μετά την επίσκεψη με τη χρήση εξειδικευμένου κοινωνικού δικτύου, φτιαγμένου ειδικά για τους επισκέπτες του μουσείου.)
    Keywords
    -
  20. [j58]
    Vassilakis, C. Blockchain technologies for leveraging security and privacy. In Homo Virtualis, 2 (1): 7-14, 2019.Abstract & details Full text DOI: http://dx.doi.org/10.12681/homvir.20188 BibTeX
    Abstract
    The contemporary internet has developed into a complex ecosystem involving humans, services, applications, machines and applications that interact exchanging information, ranging from e-mail messages and social media content to crowdsourcing data and videoconferencing. In this context, a number of security threats such as viruses and malware exist, while additionally the users’ privacy is jeopardized by threats such as personal data leakage, usage pattern monitoring, and so forth. The IoT trend renders the Internet ecosystem even more complex, by adding a rich set of services, applications and machines, many of them backed by new user roles; these elements are weaved into everyday life and industry alike. This increases both the number of opportunities available to threat agents for exploitation and the volume and value of the underlying infrastructure and data, increasing thus the user risk level. In this paper, we explore how the Blockchain technology can be used to leverage security and privacy in the modern Internet, both by providing underpinnings for preventive measures and by facilitating digital forensic evidence collection storage, safeguarding and controlled access.
    Keywords
    blockchain; privacy; security; internet of things

2018

  1. [j57]
    Poulopoulos, V.; Vassilakis, C.; Antoniou, A.; Lepouras, G.; Theodoropoulos, A. and Wallace, M. The personality of the influencers, the characteristics of qualitative discussions and their analysis for recommendations to cultural institutions. In Heritage, 1 (2): 239-253, 2018.Abstract & details Full text DOI: 10.3390/heritage1020016 BibTeX
    Abstract
    Social media usage is affecting peoples’ views through opinion sharing, a fact that has started to attract cultural institutions, as it is possible that this procedure can possibly be a part of a museum experience. As the main goal of a cultural institution is the maximization of senses stimulation, the device that is offered to the visitors’ hands everyday and every moment, becomes an important tool for the art spaces. In this notion we perform research on issues that can be of great importance for the museum’s online presence and attraction. We focus on establishing the personality of influencers related to culture, as well as the characteristics of qualitative discussions on the social media. Crosscult Project is an EU funded project, that aims to spur a change in the way European citizens appraise History, and sets that basis of our research as the experiments are conducted within its scope of. Through the experimental procedure, we collect information in order to define the character of the influencer and the substances of a “serious” conversation. “Serious” conversations are regarded the ones in which a cultural organization can participate actively and benefit from the participation. We present the results of our experimental evaluation and analyze how cultural institutions can benefit from the outcomes of our research.
    Keywords
    personalization; user modeling; personality traits; social media influencers; cultural informatics; serious conversations; digital humanities
  2. [c104]
    Poulopoulos, V.; Vassilakis, C.; Antoniou, A.; Wallace, M.; Lepouras, G. and Nores, M. L. ExhiSTORY: IoT in the service of Cultural Heritage. In Proceedings of the Global Information Infrastructure and Networking Symposium (GIIS 2018), Special Session on IoT and Cultural Heritage Protection, IEEE, 2018.Abstract & details DOI: 10.1109/GIIS.2018.8635759 BibTeX
    Abstract
    Creating stories for exhibitions is a fascinating and in parallel laborious task. As every exhibition is designed to tell a story, museum curators are responsible for analyzing each exhibit in order to extract messages that form a story and position accordingly the objects in correct order within the museum space. In this context, we analyze how the technological advances in the fields of sensors and the Internet of Things can be utilized in order to construct a “smart space”, where exhibits can communicate with the visitors and to each other and can be organized automatically so that they can generate rich, personalized, coherent and highly stimulating experiences. We present the architecture of the system named “exhiSTORY”, that intends to provide the appropriate infrastructure to be used in museums and places where exhibitions are held, in order to support smart exhibits. We discuss and analyze the architecture of the system and the ways of its application in a cultural space.
    Keywords
    -
  3. [bc10]
    Vassilakis, C.; Poulopoulos, V.; Antoniou, A.; Wallace, M.; Lepouras, G. and Nores, M. L. exhiSTORY: Smart self-organizing exhibits. In Big Data Platforms and Applications, Springer, 2018.Abstract & details BibTeX
    Abstract
    Creating stories for exhibitions is a fascinating and in parallel laborious task. As every exhibition is designed to tell a story, museum curators are responsible for identifying, for each exhibit, its aspects that fit to the message of the story and position the exhibit at the right place in the story thread. In this context we analyze how the technological advances in the fields of sensors and Internet of Things can be utilized in order to construct a "smart space", which consists of self-organizing exhibits that cooperate with each other and provide visitors with comprehensible, rich, diverse, personalized and highly stimulating experiences. We present the system named "exhiSTORY" that intends to provide the appropriate infrastructure to be used in museums and places where exhibitions are held in order to support smart exhibits. The architecture of the system and its application potential is presented and discussed.
    Keywords
    IoT, Sensors, Cultural heritage, Self-organized exhibitions, Smart Exhibits
  4. [c103]
    Antoniou, A.; Vassilakis, C.; Theodoropoulos, A. and Lepouras, G. The Human Computer Interaction and Virtual Reality Lab (University of Peloponnese): overview and current challenges. In Proceedings of the “Cultural informatics research and applications: State of the art and open challenges” workshop, within the Euromed 2018 Conference, 2018.Abstract & details Full text BibTeX
    Abstract
    The Human-Computer Interaction and Virtual Reality Lab, at the Department of Informatics and Telecommunications of the University of Peloponnese, aims to conduct high quality research in areas related to the analysis, design, develop-ment, and evaluation of HCI and VR systems and applications, and in parallel to support the teaching requirements of the department in the respective field. Over the last years the HCI-VR lab particularly focuses on Cultural Heritage and de-velops technologies primarily for spaces of cultural heritage that cover the diverse needs of heterogeneous audiences providing holistic visitor experience. The HCI-VR lab is actively participating in National and European projects on Cultural Heritage, such as FP7 Experimedia (https://hci-vr.dit.uop.gr/experimedia), H2020 CrossCult (www.crosscult.eu) and multiple projects from the National Strategic Reference Framework.
    Keywords
    -
  5. [c102]
    Poulopoulos, V.; Vassilakis, C.; Antoniou, A.; Lepouras, G. and Wallace, M. Personality Analysis of Social Media Influencers as a Tool for Cultural Institutions. In Digital Heritage. Progress in Cultural Heritage: Documentation, Preservation, and Protection, pages 236-247, Springer International Publishing, 2018.Best paper awardAbstract & details DOI: 10.1007/978-3-030-01762-0_20 BibTeX
    Abstract
    Nowadays, more and more cultural venues tend to utilize social media as a main tool for marketing, spreading their messages, engaging public and raising public awareness towards culture. It comes to a point where the massive of content in social media makes it a tedious procedure to contact the appropriate audience, the people that would really be stimulated by cultural information. In this notion, we assume that establishing conversations of high impact can possibly guide the cultural venues to audiences that can benefit more. These conversations usually include the so called influencers, users whose opinion can affect many people on social media; the latter usually referred to as followers. In this research paper we examine the characteristics of the influencers that can affect the procedures of a cultural venue on social media. The research is done within the scope of "CrossCult" EU funded project.
    Keywords
    user modeling, personality traits, influencers, cultural informatics, social media
  6. [c101]
    Poulopoulos, V.; Vassilakis, C.; Wallace, M.; Antoniou, A. and Lepouras, G. The Effect of Social Media Trending Topics Related to Cultural Venues' Content. In 2018 13th International Workshop on Semantic and Social Media Adaptation and Personalization (SMAP), IEEE, 2018.Abstract & details DOI: 10.1109/SMAP.2018.8501878 BibTeX
    Abstract
    Social media have gained the majority of attention on the Internet having an extreme number of daily visitors worldwide. The amount of information exchanged is vast, while users have become equally producers and consumers of data. Words like “trending”, “influencers”, “likes” and “viral” are in the daily agenda of data analyzers, as they are associated with factors that play an important role in the influence of social media content to its audience. These aspects are nowadays strongly taken into account by organizations that want to draw the public’s attention to the content they deliver, and in this context cultural institutions have already started to take under great consideration not only their presence in social media, but also the exploitation of social media dynamics. In this paper we propose a method that can enable cultural venues to benefit from matches between their own content and ongoing discussions on social media. More specifically we extract trending topics that can be related semantically with the content of a cultural institute and examine how a venue can benefit by exploiting these matches. The proposed algorithm has been developed in the scope of the “CrossCult” H2020 project, and has been experimentally tested by analyzing the case of Twitter in Greek language.
    Keywords
    trending topics, cultural venues, cultural informatics, social media, personalization
  7. [c100]
    Margaris, D. and Vassilakis, C. Improving Collaborative Filtering’s Rating Prediction Accuracy by Considering Users’ Rating Variability. In 2018 IEEE 16th Intl Conf on Dependable, Autonomic and Secure Computing, 16th Intl Conf on Pervasive Intelligence and Computing, 4th Intl Conf on Big Data Intelligence and Computing and Cyber Science and Technology Congress(DASC/PiCom/DataCom/CyberSciTech), IEEE, 2018.Abstract & details Full text DOI: 10.1109/DASC/PiCom/DataCom/CyberSciTec.2018.00145 BibTeX
    Abstract
    When rating predictions are computed in user-user collaborative filtering, each individual rating is typically adjusted by the mean of the ratings entered by the specific user. This practice takes into account the fact that users follow different rating practices, in the sense that some are stricter when rating items, while others are more lenient. However, users’ rating practices may also differ in rating variability, in the sense that some user may be entering ratings close to her mean, while another user may be entering more extreme ratings, close to the limits of the rating scale. In this work, we (1) propose an algorithm that considers users’ ratings variability in the rating prediction computation process, aiming to improve rating prediction quality and (2) evaluate the proposed algorithm against seven widely used datasets considering three widely used variability measures and two user similarity metrics. The proposed algorithm, using the “mean absolute deviation around the mean” variability measure, has been found to intro-duce considerable gains in rating prediction accuracy, in every dataset and under both user similarity metrics tested.
    Keywords
    Collaborative Filtering, Users’ Ratings Variability, Pearson Correlation Coefficient, Cosine Similarity, Evaluation
  8. [c99]
    Margaris, D. and Vassilakis, C. Improving Collaborative Filtering’s Rating Prediction Coverage in Sparse Datasets by Exploiting User Dissimilarity. In 2018 IEEE 16th Intl Conf on Dependable, Autonomic and Secure Computing, 16th Intl Conf on Pervasive Intelligence and Computing, 4th Intl Conf on Big Data Intelligence and Computing and Cyber Science and Technology Congress(DASC/PiCom/DataCom/CyberSciTech), IEEE, 2018.Abstract & details Full text DOI: 10.1109/dasc/picom/datacom/cyberscitec.2018.00150 BibTeX
    Abstract
    Collaborative filtering systems analyze the ratings databases to identify users with similar likings and preferences, termed as near neighbors, and then generate rating predictions for a user by examining the ratings of his near neighbors for items that the user has not yet rated; based on rating predictions, recommenda-tions are then formulated. However, these systems are known to exhibit the “gray sheep” problem, i.e. the situation where no near neighbors can be identified for a number of users, and hence no recommendation can be formulated for them. This problem is more intense in sparse datasets, i.e. datasets with relatively small number of ratings, compared to the number of users and items. In this work, we propose a method for alleviating this problem by exploiting user dissimilarity, under the assumption that if some users have exhibited opposing preferences in the past, they are likely to do so in the future. The proposed method has been eval-uated against seven widely used datasets and has been proven to be particularly effective in increasing the percentage of users for which personalized recommendations can be formulated in the context of sparse datasets, while at the same time maintaining or slightly improving rating prediction quality.
    Keywords
    Collaborative Filtering, Sparse Datasets, User-User Correlation, Pearson Correlation Coefficient, Negative Correlation, Evaluation
  9. [j56]
    Margaris, D. and Vassilakis, C. Enhancing Rating Prediction Quality Through Improving the Accuracy of Detection of Shifts in Rating Practices. In Transactions on Large-scale Data and Knowledge-Centered Systems, 10940 (LNCS) (XXXVII): 151-191, 2018.Abstract & details Full text DOI: 10.1007/978-3-662-57932-9_5 BibTeX
    Abstract
    The most widely used similarity metrics in collaborative filtering, namely the Pearson Correlation and the Adjusted Cosine Similarity, adjust each individual rating by the mean of the ratings entered by the specific user, when computing similarities, due to the fact that users follow different rating practices, in the sense that some are stricter when rating items, while others are more lenient. However, a user’s rating practices change over time, i.e. a user could start as lenient and subsequently become stricter or vice versa; hence by relying on a single mean value per user, we fail to follow such shifts in users’ rating practices, leading to decreased rating prediction accuracy. In this work, we present a novel algorithm for calculating dynamic user averages, i.e. time-in-point averages that follow shifts in users’ rating practices, and exploit them in both user-user and item-item collaborative filtering implementations. The proposed algorithm has been found to introduce significant gains in rating prediction accuracy, and outperforms other dynamic average computation approaches that are presented in the literature.
    Keywords
    Recommender systems; Collaborative filtering; User-user similarity; Item-item similarity; Dynamic average; Prediction accuracy; Ratings’ timestamps
  10. [c98]
    Mathas, C. M.; Segou, O. E.; Xylouris, G.; Christinakis, D.; Kourtis, M-A.; Vassilakis, C. and Kourtis, A. Evaluation of Apache Spot’s machine learning capabilities in an SDN/NFV enabled environment. In Proceedings of the 13th International Conference on Availability, Reliability and Security - ARES 2018, ACM Press, 2018.Abstract & details DOI: 10.1145/3230833.3233278 BibTeX
    Abstract
    Software Defined Networking (SDN) and Network Function Virtualisation (NFV) are transforming modern networks towards a service-oriented architecture. At the same time, the cybersecurity industry is rapidly adopting Machine Learning (ML) algorithms to improve detection and mitigation of complex attacks. Traditional intrusion detection systems perform signature-based detection, based on well-known malicious traffic patterns that signify potential attacks. The main drawback of this method is that attack patterns need to be known in advance and signatures must be preconfigured. Hence, typical systems fail to detect a zero-day attack or an attack with unknown signature. This work considers the use of machine learning for advanced anomaly detection, and specifically deploys the Apache Spot ML framework on an SDN/NFV-enabled testbed running cybersecurity services as Virtual Network Functions (VNFs). VNFs are used to capture traffic for ingestion by the ML algorithm and apply mitigation measures in case of a detected anomaly. Apache Spot utilises Latent Dirichlet Allocation to identify anomalous traffic patterns in Netflow, DNS and proxy data. We evaluate the overall performance of Apache Spot by deploying Denial of Service (Slowloris, BoNeSi) and a Data Exfiltration attack (iodine).
    Keywords
    Software Defined Networking, Network Function Virtualisation, Machine Learning, Latent Dirichlet Allocation, Apache Spot, Penetration Testing, SHIELD Project�
  11. [j55]
    Margaris, D. and Vassilakis, C. Exploiting Rating Abstention Intervals for Addressing Concept Drift in Social Network Recommender Systems. In Informatics, 5 (2): 21 pages, 2018.Abstract & details Full text DOI: 10.3390/informatics5020021 BibTeX
    Abstract
    One of the major problems that social networks face is the continuous production of successful, user-targeted information in the form of recommendations, which are produced exploiting technology from the field of recommender systems. Recommender systems are based on information about users’ past behavior to formulate recommendations about their future actions. However, as time goes by, social network users may change preferences and likings: they may like different types of clothes, listen to different singers or even different genres of music and so on. This phenomenon has been termed as concept drift. In this paper: (1) we establish that when a social network user abstains from rating submission for a long time, it is a strong indication that concept drift has occurred and (2) we present a technique that exploits the abstention interval concept, to drop from the database ratings that do not reflect the current social network user’s interests, thus improving prediction quality.
    Keywords
    social networks, recommender systems, collaborative filtering, shift of interest, concept drift, evaluation
  12. [j54]
    Vassilakis, C.; Poulopoulos, V.; Antoniou, A.; Wallace, M.; Lepouras, G. and Nores, M. L. exhiSTORY: Smart Exhibits That Tell Their Own Stories. In Future Generation of Computer Systems, 81: 542-556, 2018.Abstract & details Full text DOI: https://doi.org/10.1016/j.future.2017.10.038 BibTeX
    Abstract
    Museum exhibitions are designed to tell a story; this story is woven by curators and in its context a particular aspect of each exhibit, fitting to the message that the story is intended to convey, is highlighted. Adding new exhibits to the story requires curators to identify for each exhibit its aspects that fit to the message of the story and position the exhibit at the right place in the story thread. The availability of rich semantic information for exhibits, allows for exploiting the wealth of meanings that museum exhibits express, enabling the automated or semi-automated generation of practically countless stories that can be told. Personalization algorithms can then be employed to choose from these stories the ones most suitable for each individual user, based on the semantics of the stories and information within the user profile. In this work we examine how opportunities arising from technological advances in the fields of IoT and semantics can be used to develop smart, self-organizing exhibits that cooperate with each other and provide visitors with comprehensible, rich, diverse, personalized and highly stimulating experiences. These notions are included in the design of a system named exhiSTORY, which also exploits previously ignored information and identifies previously unseen semantic links. We present the architecture of the system and discuss its application potential.
    Keywords
    IoT, Cultural heritage, Self-organizing exhibitions, Semantics, Quality of Experience (QoE), personalization

2017

  1. [j53]
    Margaris, D. and Vassilakis, C. Using Time Clusters for Following Users’ Shifts in Rating Practices. In Complex Systems Informatics and Modeling Quarterly, 13, 2017.Abstract & details DOI: 10.7250/csimq.2017-13.02 BibTeX
    Abstract
    Users that enter ratings for items follow different rating practices, in the sense that, when rating items, some users are more lenient, while others are stricter. This aspect is taken into account by the most widely used similarity metric in user-user collaborative filtering, namely, the Pearson Correlation, which adjusts each individual user rating by the mean value of the ratings entered by the specific user, when computing similarities. However, a user’s rating practices change over time, i.e. a user could start as strict and subsequently become lenient or vice versa. In that sense, the practice of using a single mean value for adjusting users’ ratings is inadequate, since it fails to follow such shifts in users’ rating practices, leading to decreased rating prediction accuracy. In this work, we address this issue by using the concept of dynamic averages introduced earlier and we extend earlier work by (1) introducing the concept of rating time clusters and (2) presenting a novel algorithm for calculating dynamic user averages and exploiting them in user-user collaborative, filtering implementations. The proposed algorithm incorporates the aforementioned concept and is able to follow more successfully shifts in users’ rating practices. It has been evaluated using numerous datasets, and has been found to introduce significant gains in rating prediction accuracy, while outperforming the dynamic average computation approaches that are presented earlier.
    Keywords
    Recommender Systems, Collaborative Filtering, Rating Time Clusters, Dynamic Average, Rating Abstention Interval, Ratings’ Timestamps
  2. [c97]
    Antoniou, A.; Vassilakis, C.; Wallace, M.; Lepouras, G. and Poulopoulos, V. Experiences from the development of thematic itineraries in three Greek museums (Greek title: Εμπειρίες από την ανάπτυξη θεματικών διαδρομών σε τρία Ελληνικά μουσεία). In Proceedings of the 2nd PanHellenic conference on Cultural Heritage (Euromed 2017), 2017.(Original paper in Greek)Abstract & details BibTeX
    Abstract
    Private museums, as well as a considerable number of public regional museums, are confined by the small exhibition space and the relatively small number of exhibits and therefore cannot develop multiple exhibitions to satisfy visitors with different interests and characteristics. In this paper we report on our experieces from developing multiple thematic itineraries in the Tegea Folklore Museum , in the Cretan open-air museum "Lychnostatis" in Heraclion, and in the Panarcadic Archaeological Museum of Tripolis. The thematic itineraries in the Tegea Folklore Museum are (a) space (b) technology and (c) clothing. In the Cretan open-air museum "Lychnostatis", the itineraries are (a) natural sciences,(b) popular art, (c) pre-industrial technology and (d) folklore. In the Panarcadic Archaeological Museum of Tripolis we have the following itineraries: (a) appearance/clothing, (b) mortality, (c) nudity, (d) religion, (e) social status, (f) education, (g) healing practices and (h) everyday life. Each itinerary exploits a subset of the available exhibits to present a selected subject and is adapted to the needs of a predetermined and focused group of the general public. The results from the application of the approach, insofar, have shown that this is a promising path, both regarding the better exploitation of the space and the exhibits of the small museums, as well as regarding the better adaptation to the interests of the visitors.
    Keywords
    -
  3. [c96]
    Boukoros, S.; Nugaliyadde, A.; Marnerides, A.; Vassilakis, C.; Koutsakis, P. and Wong, K. W. Modeling Server Workloads for Campus Email Traffic Using Recurrent Neural Networks. In Proceedings of the 24th International Conference on Neural Information Processing (ICONIP 2017), pages 57-66, Springer International Publishing, 2017.Abstract & details DOI: 10.1007/978-3-319-70139-4_6 BibTeX
    Abstract
    As email workloads keep rising, email servers need to handle this explosive growth while offering good quality of service to users. In this work, we focus on modeling the workload of the email servers of four universities (2 from Greece, 1 from the UK, 1 from Australia). We model all types of email traffic, including us-er and system emails, as well as spam. We initially tested some of the most popu-lar distributions for workload characterization and used statistical tests to evaluate our findings. The significant differences in the prediction accuracy results for the four datasets led us to investigate the use of a Recurrent Neural Network (RNN) as time series modeling to model the server workload, which is a first for such a problem. Our results show that the use of RNN modeling leads in most cases to high modeling accuracy for all four campus email traffic datasets.
    Keywords
    Email traffic, Model server workload, Recurrent neural network, Time series modeling
  4. [j52]
    Vassilakis, C.; Antoniou, A.; Lepouras, G.; Poulopoulos, V.; Wallace, M.; Bampatzia, S. and Bourlakos, I. Stimulation of reflection and discussion in museum visits through the use of social media. In Social Network Analysis and Mining, 7 (40): 1-12, 2017.Abstract & details Full text DOI: 10.1007/s13278-017-0460-3 BibTeX
    Abstract
    In this paper, we examine how social media can be linked to cultural heritage and in particular how we can incorporate games, social networks, history reflection and culture. More specifically, we explore the following aspects: (a) how social media sites can be integrated into the museum user experience (b) how user interactions within the social media, both within the context of the museum experience and outside it, can be exploited to enhance the quality of recommendations made to the users, (c) how trending topics from social media can be used to link museum exhibits with today’s topics of interest and (d) how multi-level related terms extraction from social media data can lead to proposals for reflections to users. The end goal is to provide increased stimuli for users to study exhibits deeper and reflect on them, as well as to trigger discussion between the users, thus maximizing the impact of a museum visit.
    Keywords
    social networks, user profiling, cognitive style, reflection, communication, big data
  5. [j51]
    Margaris, D. and Vassilakis, C. Exploiting Internet of Things information to enhance venues' recommendation accuracy. In Service Oriented Computing and Applications, 11 (4): 393-409, 2017.Abstract & details Full text DOI: 10.1007/s11761-017-0216-y BibTeX
    Abstract
    In this paper, we introduce a novel recommendation algorithm, which exploits data sourced from web services provided by the Internet of Things in order to produce more accurate venue recommendations. The proposed algorithm provides added value for the web services offered by the Internet of Things and enhances the state-of-the-art in this algorithm category by taking into account (a) web of things data regarding the contexts of the user and the context of the venues to be recommended (restaurants, movie theatres, etc.), such as the user’s geographical position, road traffic and weather conditions, (b) qualitative aspects of the venues, such as price, atmosphere or service, (c) the semantic similarity of venues and (d) the influencing factors between social network users, derived from user participation in social networks. The combination of these features leads to more accurate and better user-targeted recommendations. We also present a framework which incorporates the above characteristics, and we evaluate the presented algorithm, both in terms of performance and recommendation quality.
    Keywords
    Internet of Things, Web Services, Recommendation Applications, Collaborative Filtering, Social Networks, Evaluation, Performance
  6. [c95]
    Bourlakos, I.; Wallace, M.; Antoniou, A.; Vassilakis, C.; Lepouras, G. and Karapanagiotou, A. V. Formalization and visualization of the narrative for museum guides. In Proceedings of the third International KEYSTONE Conference (IKC2017), Springer, 2017.Abstract & details Full text DOI: https://doi.org/10.1007/978-3-319-74497-1_1 BibTeX
    Abstract
    There is a wide range of meta-data standards for the documentation of museum related information, such as CIDOC-CRM; these standards focus on the description of distinct exhibits. In contrast, there is a lack of standards for the digitization and documentation of the routes followed and information provided by museum guides. In this work we propose the notion of the narrative, which can be used to model a guided museum visit. We provide a formalization for the narrative so that it can be digitally encoded, and thus preserved, shared, re-used, further developed and exploited, and also propose an intuitive visualization approach.
    Keywords
    -
  7. [c94]
    Margaris, D. and Vassilakis, C. Improving Collaborative Filtering’s Rating Prediction Quality by Considering Shifts in Rating Practices. In Proceedings of the 19th IEEE International Conference on business informatics (CBI17), IEEE, 2017.Abstract & details Full text DOI: 10.1109/CBI.2017.24 BibTeX
    Abstract
    Users that populate ratings databases, such as IMDB, follow different marking practices, in the sense that some are stricter, while others are more lenient. This aspect has been captured by the most widely used similarity metrics in collaborative filtering, namely the Pearson Correlation and the Adjusted Cosine Similarity, which adjust each individual rating by the mean of the ratings entered by the specific user, when computing similarities. However, relying on the mean value presumes that the users' marking practices remain constant over time; in practice though, it is possible that a user's marking practices change over time, i.e. a user could start as strict and subsequently become lenient, or vice versa. In this work, we propose an approach to take into account marking practices shifts by (1) introducing the concept of dynamic user rating averages which follow the users' marking practices shifts, (2) presenting two alternative algorithms for computing a user's dynamic averages and (3) performing a comparative evaluation among these two algorithms and the classic static average (unique mean value) that the Pearson Correlation uses.
    Keywords
    Collaborative Filtering; User-User Correlation; Dynamic Average; Prediction Quality; Ratings’ Timestamps
  8. [j50]
    Margaris, D. and Vassilakis, C. Enhancing User Rating Database Consistency Through Pruning. In Transactions on Large-Scale Data- and Knowledge-Centered Systems, LNCS, volume 10620 (Special issue on Consistency and Inconsistency in Data-centric Applications): 33-64, 2017.Abstract & details Full text DOI: 10.1007/978-3-662-55947-5_3 BibTeX
    Abstract
    Recommender systems are based on information about users' past behavior to formulate recommendations about their future actions. However, as time goes by the interests and likings of people may change: people listen to different singers or even different types of music, watch different types of movies, read different types of books and so on. Due to this type of changes, an amount of inconsistency is introduced in the database since a portion of it does not reflect the current preferences of the user, which is its intended purpose. In this paper, we present a pruning technique that removes old aged user behavior data from the ratings database, which are bound to correspond to invalidated preferences of the user. Through pruning (1) inconsistencies are removed and data quality is upgraded, (2) better rating prediction generation times are achieved and (3) the ratings database size is reduced. We also propose an algorithm for determining the amount of pruning that should be performed, allowing the tuning and operation of the pruning algorithm in an unsupervised fashion. The proposed technique is evaluated and compared against seven aging algorithms, which reduce the importance of aged ratings, and a state-of-the-art pruning algorithm, using datasets with varying characteristics. It is also validated using two distinct rating prediction computation strategies, namely collaborative filtering and matrix factorization. The proposed technique needs no extra information concerning the items' characteristics (e.g. categories that they belong to or attributes' values), can be used in all rating databases that include a timestamp and has been proved to be effective in any size of users-items database and under two rating prediction computation strategies. Note: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.
    Keywords
    Internet of Things, Web services, Recommendation applications, Collaborative filtering, Social networks, Evaluation, Performance
  9. [c93]
    Margaris, D. and Vassilakis, C. Improving Collaborative Filtering's Rating Prediction Quality in Dense Datasets, by Pruning Old Ratings. In Proceedings of the 22nd IEEE Symposium on Computers and Communications (ISCC17), IEEE, 2017.Abstract & details Full text DOI: 10.1109/ISCC.2017.8024683 BibTeX
    Abstract
    In this paper, we introduce a pruning algorithm which removes aged user ratings from the rating database used by collaborative filtering algorithms, in order to (1) improve prediction quality and (2) minimize the rating database size, as well as the rating prediction generation time. The proposed algorithm needs no extra information concerning the items' characteristics (e.g. categories that they belong to or attributes' values) and can be used with all rating databases that include a timestamp. Furthermore, we propose and validate a method for identifying the most prominent combination of a pruning algorithm and a pruning level for datasets, allowing thus to perform the selection of pruning algorithm and pruning level in an unsupervised fashion.
    Keywords
    -
  10. [j49]
    Margaris, D.; Vassilakis, C. and Georgiadis, P. Query personalization using social network information and collaborative filtering techniques. In Future Generation of Computer Systems, Special Issue on Recommender Systems for Large-Scale Social Networks: 440-450, 2017.Abstract & details Full text DOI: 10.1016/j.future.2017.03.015 BibTeX
    Abstract
    Query personalization has emerged as a means to handle the issue of information volume growth, aiming to tailor query answer results to match the goals and interests of each user. Query personalization dynamically enhances queries, based on information regarding user preferences or other contextual information; typically enhancements relate to incorporation of conditions that filter out results that are deemed of low value to the user and/or ordering results so that data of high value are presented first. In the domain of personalization, social network information can prove valuable; users’ social networks profiles, including their interests, influence from social friends, etc. can be exploited to personalize queries. In this paper, we present a query personalization algorithm, which employs collaborative filtering techniques and takes into account influence factors between social network users, leading to personalized results that are better-targeted to the user.
    Keywords
    Social networks; Personalization; Collaborative search; Database query transformation; Presentation of retrieval results
  11. [bc9]
    Margaris, D.; Vassilakis, C. and Georgiadis, P. Knowledge-Based Leisure Time Recommendations in Social Networks. In Current Trends on Knowledge-Based Systems, pages 23-48, Springer International Publishing, Intelligent Systems Reference Library , 2017.Abstract & details DOI: 10.1007/978-3-319-51905-0_2 BibTeX
    Abstract
    We introduce a novel knowledge-based recommendation algorithm for leisure time information to be used in social networks, which enhances the state-of-the-art in this algorithm category by taking into account (a) qualitative aspects of the recommended places (restaurants, museums, tourist attractions etc.), such as price, service and atmosphere, (b) influencing factors between social network users, (c) the semantic and geographical distance between locations and (d) the semantic categorization of the places to be recommended. The combination of these features leads to more accurate and better user-targeted leisure time recommendations.
    Keywords
    Knowledge-based Recommender Systems, Social Networks, Collaborative Filtering, Attribute constraints, Semantic Information
  12. [c92]
    Theodorakopoulos, M.; Papageorgopoulos, N.; Mourti, A.; Antoniou, A.; Wallace, M.; Lepouras, G.; Vassilakis, C. and Platis, N. Personalized Augmented Reality Experiences in Museums using Google Cardboards. In 2017 12th International Workshop on Semantic and Social Media Adaptation and Personalization (SMAP), IEEE CPS, 2017.Abstract & details Full text DOI: 10.1109/smap.2017.8022676 BibTeX
    Abstract
    In this short paper we examine the suitability of the Google Cardboard as a means for the delivery of personalized cultural experiences. Specifically, we develop the content and create the application required in order to provide highly personalized visits to the Archaeological Museum in Tripolis, Greece. We also examine the usability issues related to the use of Google Cardboards. Early results are promising, and based on them we also outline the next steps ahead.
    Keywords
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2016

  1. [j48]
    Margaris, D.; Vassilakis, C. and Georgiadis, P. Recommendation information diffusion in social networks considering user influence and semantics. In Social Network Analysis and Mining, 6 (1): 108, 2016.Abstract & details Full text DOI: 10.1007/s13278-016-0416-z BibTeX
    Abstract
    One of the major problems in the domain of social networks is the handling and diffusion of the vast, dynamic and disparate information created by its users. In this context, the information contributed by users can be exploited to generate recommendations for other users. Relevant recommender systems take into account static data from users' profiles, such as location, age or gender, complemented with dynamic aspects stemming from the user behavior and/or social network state such as user preferences, items' general acceptance and influence from social friends. In this paper, we enhance recommendation algorithms used in social networks by taking into account qualitative aspects of the recommended items, such as price and reliability, the influencing factors between social network users, the social network user behavior regarding their purchases in different item categories and the semantic categorization of the products to be recommended. The inclusion of these aspects leads to more accurate recommendations and diffusion of better user-targeted information. This allows for better exploitation of the limited recommendation space, and therefore online advertisement efficiency is raised.
    Keywords
    Information diffusion, Social networks, Collaborative filtering, Quality of service, Semantic information
  2. [c91]
    Margaris, D. and Vassilakis, C. Pruning and Aging for User Histories in Collaborative Filtering. In Proceedings of the 2016 IEEE Symposium Series on Computational Intelligence, 2016.Abstract & details Full text DOI: 10.1109/ssci.2016.7849920 BibTeX
    Abstract
    In this paper, we introduce algorithms for pruning and aging user ratings in collaborative filtering systems, based on their oldness, under the rationale that aged user ratings may not accurately reflect the current state of users regarding their preferences. The aging algorithm reduces the importance of aged ratings, while the pruning algorithm removes them from the database. The algorithms are evaluated against various types of datasets. The pruning algorithm has been found to present a number of advantages, namely (1) reducing the rating database size, (2) achieving better prediction generation times and (3) improving prediction quality by cutting off predictions with high error. The algorithm can be used in all rating databases that include a timestamp and has been proved to be effective in any type of dataset, from movies and music, to videogames and books.
    Keywords
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  3. [c90]
    Bampatzia, S.; Bravo-Quezada, O. G.; Antoniou, A.; Nores, M. L.; Wallace, M.; Lepouras, G. and Vassilakis, C. The use of semantics in the CrossCult H2020 project. In Proceedings of the second International KEYSTONE Conference, (IKC2016), pages 190-195, 2016.Abstract & details Full text DOI: https://doi.org/10.1007/978-3-319-53640-8_17 BibTeX
    Abstract
    CrossCult is a newly started project that aims to make reflective history a reality in the European cultural context. In this paper we examine how the project aims to take advantage of advances in semantic technologies in order to achieve its goals. Specifically, we see what the quest for reflection is and, through practical examples from two of the project's flagship pilots, explain how semantics can assist in this direction
    Keywords
    -
  4. [c89]
    Bampatzia, S.; Antoniou, A.; Lepouras, G.; Vassilakis, C. and Wallace, M. Using social media to stimulate history reflection in cultural heritage. In 2016 11th International Workshop on Semantic and Social Media Adaptation and Personalization (SMAP), IEEE, 2016.Abstract & details Full text DOI: 10.1109/smap.2016.7753390 BibTeX
    Abstract
    CrossCult H2020 is a European project, the aim of which is the reflection of history in a cultural setting. In this paper, we describe how social media can be linked to cultural heritage and in particular how we can incorporate games, social networks, history reflection and culture. The paper presents the case study of one of the project pilots, to show how history reflection can be enhanced with the use of social networks.
    Keywords
    -
  5. [c88]
    Margaris, D.; Vassilakis, C. and Georgiadis, P. Improving QoS Delivered by WS-BPEL Scenario Adaptation through Service Execution Parallelization. In Proceedings of the 31st Annual ACM Symposium on Applied Computing, pages 1590-1596, ACM, 2016.Abstract & details Full text DOI: 10.1145/2851613.2851805 BibTeX
    Abstract
    WS-BPEL scenario execution adaptation has been proposed by researchers as a response to the need of users to tailor the WS-BPEL scenario execution to their individual preferences; these preferences are typically expressed through Quality of Service (QoS) policies, which the adaptation mechanism considers in order to select the services that will ultimately be invoked to realize the desired business process. In this paper, we study the potential to parallelize the execution of the WS-BPEL scenario in order to minimize its response time and/or achieving higher scores in the other qualitative dimensions, such as cost, reliability, etc., at the same time. We also describe, develop and validate a parallelization algorithm for realizing the proposed enhancements.
    Keywords
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  6. [c87]
    Bampatzia, S.; Bourlakos, I.; Antoniou, A.; Vassilakis, C.; Lepouras, G. and Wallace, M. Serious Games: Valuable Tools for Cultural Heritage. In Proceedings of the 2016 Games and Learning Alliance Conference, pages 331-341, Springer International Publishing, 2016.Abstract & details Full text DOI: https://doi.org/10.1007/978-3-319-50182-6_30 BibTeX
    Abstract
    Wishing to connect cultural heritage, games and social networks, the present work describes games to be used within the framework of a European H2020 project. For the purposes of supporting the museum visit, before, during and after, 5 games were designed for social networks to accomplish user profil-ing, to promote the museum and the application through social network dissemi-nation, to introduce museum items and themes and to also function as visit sou-venirs. The games are also presented in a generic framework for games in cultural heritage, which has been used successfully in the past.
    Keywords
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  7. [c86]
    Vassilakis, C.; Antoniou, A.; Lepouras, G.; Wallace, M.; Lykourentzou, I. and Naudet, Y. Interconnecting Objects, Visitors, Sites and (Hi)Stories Across Cultural and Historical Concepts: The CrossCult Project. In Digital Heritage. Progress in Cultural Heritage: Documentation, Preservation, and Protection, pages 501-510, Springer International Publishing, 2016.Abstract & details Full text DOI: 10.1007/978-3-319-48496-9_39 BibTeX
    Abstract
    Human History, is a huge mesh of interrelated facts and concepts, spanning beyond borders, encompassing global aspects and finally constituting a shared, global experience. This is especially the case regarding European history, which is highly interconnected by nature; however, most History-related experiences that are today offered to the greater public, from schools to museums, are siloed. The CrossCult project aims to provide the means for offering citizens and cultural venue visitors a more holistic view of history, in the light of cross-border interconnections among pieces of cultural heritage, other citizens viewpoints and physical venues. To this end, the CrossCult project will built a comprehensive knowledge base encompassing information and semantic relationships across cultural information elements, and will provide the technological means for delivering the contents of this knowledge base to citizens and venue visitors in a highly personalized manner, creating narratives for the interactive experiences that maximise situational curiosity and serendipitous learning. The CrossCult platform will also exploit the cognitive/emotional profiles of the participants as well as temporal, spatial and miscellaneous features of context, including holidays and anniversaries, social media trending topics and so forth.
    Keywords
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2015

  1. [c85]
    Masselos, K.; Vassilakis, C.; Lepouras, G.; Trifonopoulos, C.; Tselikas, N. and Platis, N. A mobile-enabled platform for presenting and disseminating cultural heritage information enhanced with augmented reality (Greek title: ΜΙΑ ΠΛΑΤΦΟΡΜΑ ΓΙΑ ΠΑΡΟΥΣΙΑΣΗ ΚΑΙ ΔΙΑΧΥΣΗ ΠΛΗΡΟΦΟΡΙΩΝ ΠΟΛΙΤΙΣΤΙΚΗΣ ΚΛΗΡΟΝΟΜΙΑΣ ΜΕ ΥΠΟΣΤΗΡΙΞΗ ΓΙΑ ΚΙΝΗΤΕΣ ΣΥΣΚΕΥΕΣ ΚΑΙ ΕΜΠΛΟΥΤΙΣΜΕΝΗ ΜΕ ΕΠΑΥΞΗΜΕΝΗ ΠΡΑΓΜΑΤΙΚΟΤΗΤΑ). In 1st Panhellenic Conference on Cultural Heritage Digitization, 2015.(Original paper in Greek)Abstract & details BibTeX
    Abstract
    The advent of mobile technologies has created opportunities for more effective delivery of cultural heritage information to all interested parties, and especially tourists who are on-the-move. Many people nowadays are equipped with smartphones or tablets equipped with location tracking devices such as GPS and compasses and having internet access available; these smartphones can be used for efficient delivery of cultural heritage information, in a personalized and timely fashion. Moreover, the computing resources of these smartphones are adequate to enable the use of augmented reality techniques, which provide a lively and engaging experience to the users. However, the same content still needs to be disseminated to users of stationary computers. In this paper, we report on the design and development of a mobile-enabled platform for presenting and disseminating cultural heritage information enhanced with augmented reality and integration with social networks.
    Keywords
    -
  2. [c84]
    Margaris, D.; Panagiotis, G. and Costas, V. On Replacement Service Selection in WS-BPEL Scenario Adaptation. In Proceedings of the 8th IEEE International Conference on Service Oriented Computing & Applications (SOCA 2015), IEEE, 2015.Abstract & details DOI: 10.1109/SOCA.2015.11 BibTeX
    Abstract
    WS-BPEL scenario execution adaptation has been proposed by numerous researchers as a response to the need of users to tailor the WS-BPEL scenario execution to their individual preferences; these preferences are typically expressed through Quality of Service (QoS) policies, which the adaptation mechanism considers in order to select the services that will ultimately be invoked to realize the desired business process. In this paper, we consider a number of issues related to WS-BPEL scenario adaptation, aiming to enhance adaptation quality and improve the QoS offered to end users. More specifically, with the goal of broadening the service selection pool we (a) discuss the identification of potential services that can be used to realize a functionality used in the WS-BPEL scenario and (b) elaborate on transactional semantics that invocations to multiple services offered by the same provider may bear. We also describe and validate an architecture for realizing the proposed enhancements.
    Keywords
    -
  3. [j47]
    Katifori, A.; Vassilakis, C.; Lepouras, G. and Torou, E. Effectiveness of visualization for information retrieval through ontologies with entity evolution: the impact of ontology modeling. In International Journal of Information Retrieval Research, 5 (2): 66-91, 2015.Abstract & details DOI: 10.4018/IJIRR.2015040104 BibTeX
    Abstract
    Incorporating digital tools in the business and scientific research workflows is at the moment an on-going process, challenging and demanding as every domain has its own needs in terms of data models and information retrieval methods. The information in some domains involves entity evolution, a characteristic that introduces additional tasks, such as finding all evolution stages of an entity, and poses additional requirements for the information retrieval process. In this paper, we present a user study aiming to investigate how the different aspects of ontology modelling affect the performance and effectiveness of users regarding information retrieval tasks that are carried out using visualization methods. The results of the user study are analyzed and guidelines for ontology design are offered.
    Keywords
    Effectiveness, Entity Evolution, Information Retrieval, Ontology Modeling, User Study, Visualization for Information Retrieval
  4. [c83]
    Margaris, D.; Georgiadis, P. and Vassilakis, C. A Collaborative Filtering Algorithm with Clustering for Personalized Web Service Selection in Business Processes. In Proceedings of RCIS 2015, 2015.Abstract & details DOI: 10.1109/RCIS.2015.7128877 BibTeX
    Abstract
    Recommender systems aim to propose items that are expected to be of interest to the users. As one of the most successful approaches to building recommender systems, collaborative filtering exploits the known preferences of a group of users to formulate recommendations or predictions of the unknown preferences for other users. In many cases, collaborative filtering algorithms handle complex items, which are described using hierarchical tree structures containing rich semantic information. In order to make accurate recommendations on such items, the related algorithms must examine all aspects of the available semantic information. Thus, when collaborative filtering techniques are employed to adapt the execution of business processes, they must take into account the services’ Quality of Service parameters, so as to generate recommendations tailored to the individual user needs. In this paper, we present a collaborative filtering-based algorithm which takes into account the web services’ QoS parameters in order to tailor the execution of business processes to the preferences of users. An offline clustering technique is also introduced for supporting the efficient and scalable execution of proposed algorithm under the presence of large repositories of sparse data.
    Keywords
    collaborative filtering; clustering; business processes; web services; quality of service; hierarchical tree; performance
  5. [c82]
    Margaris, D.; Vassilakis, C. and Georgiadis, P. A Hybrid Framework for WS-BPEL Scenario Execution Adaptation, Using Monitoring and Feedback Data. In Proceedings of the 30th ACM/SIGAPP Symposium On Applied Computing, SOAP track, ACM, 2015.Abstract & details Full text DOI: 10.1145/2695664.2695687 BibTeX
    Abstract
    In this paper, we present a framework which provides runtime adaptation for BPEL scenarios. The adaptation is based on (a) quality of service parameters of available web services (b) quality of service policies specified by users (c) collaborative filtering techniques, allowing clients to further refine the adaptation process by considering service selections made by other clients, (d) monitoring, in order to follow the variations of QoS attribute values and (e) on users’ opinions services they have used.
    Keywords
    -
  6. [j46]
    Margaris, D.; Vassilakis, C. and Georgiadis, P. An integrated framework for adapting WS-BPEL scenario execution using QoS and collaborative filtering techniques. In Science of Computer Programming, 98: 707-734, 2015.Abstract & details Full text DOI: 10.1016/j.scico.2014.10.007 BibTeX
    Abstract
    In this paper, we present a framework which incorporates runtime adaptation for BPEL scenarios. The adaptation is based on (a) the quality of service parameters of available services, allowing for tailoring their execution to the diverse needs of individual users and (b)collaborative filtering techniques, allowing clients to further refine the adaptation process by considering service selections made by other clients, in the context of the same business processes. The proposed framework also caters maintaining the transactional semantics that invocations to multiple services offered by the same provider may bear.
    Keywords
    WS-BPEL; Adaptation; Quality of service; Collaborative filtering; Metasearch algorithms

2014

  1. [c81]
    Katifori, A.; Vassilakis, C.; Lepouras, G. and Halatsis, C. Visualization method effectiveness in ontology-based information retrieval tasks involving entity evolution. In Proceedings of SMAP 2014, 2014.Abstract & details DOI: 10.1109/SMAP.2014.24 BibTeX
    Abstract
    Incorporating digital tools in the business and scientific research workflows is at the moment an on-going process, challenging and demanding as every domain has its own needs in terms of data models and information retrieval methods. The information in some domains involves entity evolution, a characteristic that introduces additional tasks, such as finding all evolution stages of an entity, and poses additional requirements for the information retrieval process. In this paper we present a user study aiming to investigate the effectiveness of current ontology browsing and visualization methods for supporting users in tasks involving research on entity evolution.
    Keywords
    -
  2. [c80]
    Lepouras, G.; Katifori, A.; Vassilakis, C.; Antoniou, A. and Platis, N. Towards a Learning Analytics Platform for Supporting the Educational Process. In Proceedings of the 5th Conference on Information, Intelligence, Systems & Application (IISA2014), 2014.Abstract & details Full text DOI: 10.1109/IISA.2014.6878750 BibTeX
    Abstract
    In this paper, we present the vision of an open source learning analytics platform, able to harvest data from different sources, including e-learning platforms and environments, registrar's information systems, alumni systems, etc., so as to provide all stakeholders with the necessary functionality to make decisions on the learning process. The platform's architecture is modular, allowing the introduction of new functionality or connection to new systems to collect needed data. All data can be analyzed and presented though interactive visualizations to find correlations between metrics, to make predictions for students or student groups, to identify best practices for instructors and let them explore 'what-if' scenarios, to offer students personalized recommendations and personalized detailed feedback, etc. Our objective is to inform and empower all stakeholders to improve the learning experience.
    Keywords
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  3. [c79]
    Rompa, J.; Tryfonopoulos, C.; Vassilakis, C. and Lepouras, G. Mindmap-Inspired Semantic Personal Information Management. In Demo at the 17th International Conference on Extending Database Technology, 2014, Athens, Greece, 2014.Abstract & details Full text DOI: 10.5441/002/edbt.2014.55 BibTeX
    Abstract
    Users nowadays need to manage large amounts of information, including documents, e-mails, contacts, and multimedia content. To facilitate the tasks of organisation, maintenance, and retrieval of personal information, a number of semantics-based methods have emerged; these methods employ (personal) ontologies as an underlying infrastructure for organising and querying the personal information space. In this paper we present OntoFM, a novel personal information management tool that offers a mindmap-inspired interface to facilitate user interactions with the information base. Besides serving as an information retrieval aid, OntoFM allows the user to specify and update the semantic links between information items, constituting thus a complete personal information management tool.
    Keywords
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2013

  1. [j45]
    Vasiliadis, D.; Rizos, G. and Vassilakis, C. Performance Tuning of Dual-priority Delta Networks through Queuing Scheduling Disciplines. In Journal of Communications Software and Systems, 9(4) (4): 222-235, 2013.Abstract & details Full text DOI: 10.24138/jcomss.v9i4.143 BibTeX
    Abstract
    Differentiated Services (DiffServ) and other scheduling strategies are now widespread in the traditional, “best effort” Internet. These Internet Architectures offer Quality of Service (QoS) guarantees for important customers at the same time as supporting less critical applications of lower priority. Strict priority queuing (PQ), weighted round robin (WRR), and class-based weighted fair queuing (CBWFQ) are three common scheduling disciplines for differentiation of services in telecommunication networks. In this paper, a comparative performance study of the above PQ, WRR and CBWFQ queuing scheduling policies applied on a double-buffered, 6-stage Multistage Interconnection Network (MIN) that natively supports a 2-class priority mechanism is presented and analyzed using simulation experiments. We also consider a 10-stage MIN, to validate that the conclusions drawn from the 6-stage MIN apply to MINs of different sizes. The findings of this paper can be used by MIN designers to optimally configure their networks.
    Keywords
    Diffserv networks, Multiple access scheduling algorithms, Multistage Interconnection Networks, Performance Evaluation, Simulation
  2. [c78]
    Antoniou, A.; Lykourentzou, I.; Rompa, J.; Tobias, E.; Lepouras, G.; Vassilakis, C. and Naudet, Y. User Profiling: Towards a Facebook Game that Reveals Cognitive Style. In Proceedings of the GALA 2013 conference, pages 349-353, Paris, FR, 2013.Abstract & details DOI: 10.1007/978-3-319-12157-4_28 BibTeX
    Abstract
    This paper presents an innovative approach based on social-network gaming, which will extract players? cognitive styles for personalization purposes. Cognitive styles describe the way individuals think, perceive and remember information and can be exploited to personalize user interaction. Questionnaires are usually employed to identify cognitive styles, a tedious process for most users. Our approach relies on a Facebook game for discovering potential visitors? cognitive styles with an ultimate goal of enhancing the overall visitors' experience in the museum. By hosting such a game on the museum?s webpage and on Facebook, the museum aims to attract new visitors, as well as to support the user profiling process.
    Keywords
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  3. [c77]
    Lykourentzou, I.; Claude, X.; Naudet, Y.; Tobias, E.; Antoniou, A.; Lepouras, G. and Vassilakis, C. Improving museum visitors' Quality of Experience through intelligent recommendations: A visiting style-based approach. In Proceedings of MASIE 2013 Workshop, co-located with the 9th International Conference on Intelligent Environments IE'13, Athens, GR, 2013.Abstract & details DOI: 10.3233/978-1-61499-286-8-507 BibTeX
    Abstract
    This paper investigates the effect that smart routing and recommendations can have on improving the Quality of Experience of museum visitors. The novelty of our approach consists of taking into account not only user interests but also their visiting styles, as well as modeling the museum not as a sterile space but as a location where crowds meet and interact, impacting each visitor?s Quality of Experience. The investigation is done by an empirical study on data gathered by a custom-made simulator tailored for the museum user routing problem. Results are promising and future potential and directions are discussed.
    Keywords
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  4. [c76]
    Margaris, D.; Vassilakis, C. and Georgiadis, P. An integrated framework for QoS-based adaptation and exception resolution in WS-BPEL scenarios. In Proceedings of the 28th Annual ACM Symposium on Applied Computing - SAC ’13, ACM Press, 2013.Abstract & details DOI: 10.1145/2480362.2480714 BibTeX
    Abstract
    In this paper, we present a framework which incorporates runtime quality of service-based adaptation for BPEL scenarios, allowing for tailoring their execution to the diverse needs of individual users. The proposed framework also caters for automatically resolving system-level exceptions, such as machine outages or network partitionings, while both scenario execution adaptation and exception resolution maintain the transactional semantics that invocations to multiple services offered by the same provider may bear.
    Keywords
    -
  5. [c75]
    Margaris, D.; Georgiadis, P. and Vassilakis, C. Adapting WS-BPEL scenario execution using collaborative filtering techniques. In IEEE 7th International Conference on Research Challenges in Information Science (RCIS), IEEE, 2013.Abstract & details DOI: 10.1109/rcis.2013.6577691 BibTeX
    Abstract
    WS-BPEL has been adopted as the predominant method for composing individual web services into higher-level business processes. The designers of WS-BPEL scenarios define at development time the specific web services that will be invoked in the context of the business process they model; in the context however of the current web, where each functionality is offered by multiple service providers, under different quality of service parameters, using a fixed BPEL scenario has been recognized to be inadequate for servicing the diverse needs of business processes clients. To this end, WS-BPEL scenario execution adaptation has been proposed, mainly allowing clients to specify quality of service policies, which drive the dynamic selection of the services that will be invoked. In this paper, we present a framework extending the quality of service-based adaptation mechanisms with collaborative filtering techniques, allowing clients to further refine the adaptation process by considering service selections made by other clients, in the context of the same business processes.
    Keywords
    -
  6. [j44]
    Vasiliadis, D. C.; Rizos, G. E. and Vassilakis, C. Modelling and performance study of finite-buffered blocking multistage interconnection networks supporting natively 2-class priority routing traffic. In Journal of Network and Computer Applications, 36(2) (2): 723-737, 2013.Abstract & details DOI: 10.1016/j.jnca.2012.12.016 BibTeX
    Abstract
    Contemporary networks accommodate handling of multiple priorities, aiming to provide suitable QoS levels to different traffic classes. In the presence of multiple priorities, a scheduling algorithm is employed to select each time the next packet to transmit over the data link. Class-based Weighted Fair Queuing (CBWFQ) scheduling and its variations, is widely used as a scheduling technique, since it is easy to implement and prevents the low-priority queues from being completely neglected during periods of high-priority traffic. By using this scheduling, low-priority queues have the opportunity to transmit packets even though the high-priority queues are not empty. In this paper, the modeling, analysis and performance evaluation of a single-buffered, dual priority multistage interconnection network (MIN) operating under the CBWFQ scheduling policy is presented. Performance evaluation is conducted through simulation, and the performance measures obtained can be valuable assets for MIN designers, in order to minimize the overall deployment costs and delivering efficient systems.
    Keywords
    Multistage interconnection networks; Banyan switches; Packet switching; Quality of service; Priority; Performance analysis; Simulation model
  7. [j43]
    Antoniou, A.; Lepouras, G. and Vassilakis, C. A methodology for the design of online exhibitions. In DESIDOC Journal of Library and Information Technology, 33 (3): 158-167, 2013.Abstract & details Full text DOI: 10.14429/djlit.33.4615 BibTeX
    Abstract
    The process of designing systems or products largely depends on a number of decisions, like “who do I design for?”, “what should my product do?”, “what are the user requirements?” etc. The developing teams usually base their decisions on experience and/or heuristics and this is particularly the case, in the development of online products and especially online exhibitions. The different solutions are frequently case studies of specific museums or institutions that wish to provide online content to actual or possible visitors. In addition, the interdisciplinary nature of the endeavor, involving museology, technology but also education, poses important design problems. In the following sections, we present a generic methodology for the design of online exhibitions, using top-down processes and transferable findings across museum types that wish to assist the designers during the early decision stages. This paper provides an introduction to the field, emphasising its interdisciplinary nature and reviews related work in the area of online exhibition design. It also presents an overview of the methodology, elaborating on the individual methodology steps; in particular, the processes for determining the visitors’ perception of the museum (degree of museumness); the museum needs that require to be supported; the educational approach to be adopted; the relevance to life-long learning activities; the approach to adaptivity; and user involvement have been reviewed.
    Keywords
    Online exhibitions, museums, design methodology

2012

  1. [j42]
    Vasiliadis, D. C.; Rizos, G. E. and Vassilakis, C. Class-Based Weighted Fair Queuing Scheduling on Dual-Priority Delta Networks. In Journal of Network and Computer Applications, 2012 (XX): 13 pages, 2012.Abstract & details DOI: 10.1155/2012/859694 BibTeX
    Abstract
    In this paper, we model, analyze and evaluate the performance of a 2-class priority architecture for finite-buffered Multistage Interconnection Networks (MINs). The MIN operation modelling is based on a state diagram, which includes the possible MIN states, transitions and conditions under which each transition occurs. Equations expressing state and transition probabilities are subsequently given, providing a formal model for evaluating the MIN's performance. The proposed architecture's performance is subsequently analyzed using simulations; operational parameters, including buffer length, MIN size, offered load and ratios of high priority packets which are varied across experiments to gain insight on how each parameter affects the overall MIN performance. The 2-class priority MIN performance is compared against the performance of single priority MINs, detailing the performance gains and losses for packets of different priorities. Performance is assessed by means of the two most commonly used factors, namely packet throughput and packet delay, while a performance indicator combining both individual factors is introduced, computed and discussed. The findings of this study can be used by network and interconnection system designers in order to deliver efficient systems while minimizing the overall cost. The performance evaluation model can also be applied to other network types, providing the necessary data for network designers to select optimal values for network operation parameters.
    Keywords
    -
  2. [j41]
    Vasiliadis, D. C.; Rizos, G. E. and Vassilakis, C. Class-based weighted fair queuing scheduling on quad-priority Delta Networks. In International Journal of Parallel, Emergent and Distributed Systems, 27 (5): 435-457, 2012.Abstract & details DOI: 10.1080/17445760.2012.712694 BibTeX
    Abstract
    Contemporary networks support multiple priorities, aiming to differentiate the QoS levels offered to individual traffic classes. Support for multiple priorities necessitates the introduction of a scheduling algorithm, to select each time the next packet to transmit over the data link. Class-based Weighted Fair Queuing (CBWFQ) scheduling and its variations, is widely used as a scheduling technique, since it is easy to implement and prevents the low-priority queues from starvation, i.e. receiving no service during periods of high-priority traffic. CBWFQ effectively thus offers low-priority queues the opportunity to transmit packets even though the high-priority queues are not empty. In this paper, we present the modeling and performance evaluation of a single-buffered, four-priority multistage interconnection network (MIN) operating under the CBWFQ scheduling policy. Performance evaluation is conducted through simulation, and the performance metrics obtained can be used by MIN designers to set the appropriate queue weights according to the expected traffic and the desired QoS levels for each priority class, delivering efficient thus systems.
    Keywords
    multistage interconnection networks, Delta Netwoks, performance evaluation
  3. [j40]
    Benou, P. and Vassilakis, C. A context management architecture for m-commerce applications. In Central European Journal of Computer Science, Versita, co-published with Springer Verlag, 2 (2): 87-117, 2012.Abstract & details Full text DOI: 10.2478/s13537-012-0010-z BibTeX
    Abstract
    Mobile commerce applications operate in highly dynamic environments with diverse characteristics and interesting challenges. The characteristics and conditions of these environments –called context–, can be exploited to provide adaptive mobile services, in terms of user interface, functionality and content, in order to offer more effective m-commerce. Today, building adaptive mobile services is a complex and time-consuming task due to the lack of standardized methods, tools and architectures for the identification, representation and management of the context. Addressing some of these issues, recent works have provided formal extensions for various stages of the m-commerce application lifecycle, such as extended UML class diagrams for building design models and have used context parameters in order to offer adaptive applications. Using these works as the basis, in this paper we propose a context management architecture, which accommodates the requirements that have been identified for m-commerce applications. The proposed architecture is evaluated in terms of completeness, complexity, performance and utility, and compared against other approaches proposed in the literature regarding its suitability for supporting context-aware m-commerce applications.
    Keywords
    mobile commerce, context, context-awareness, context management, adaptivity, software architecture
  4. [j39]
    Benou, P.; Vassilakis, C. and Vrechopoulos, A. Context Management for m-Commerce Applications: Determinants, Methodology and the Role of Marketing. In Information Technology and Management, 13 (2): 91-111, 2012.Abstract & details Full text DOI: 10.1007/s10799-012-0120-2 BibTeX
    Abstract
    Studying consumer behaviour and usage of environmental determinants in the mobile services domain contributes to the identification of context information which is critical for the effective operation of mobile commerce applications. Exploiting this information towards providing enhanced and innovative mobile services offers a competitive advantage within the highly demanding domain of m-commerce applications. However, in order to effectively exploit such context information, there is a need to design the necessary methods, software tools and information systems that will be employed for collecting, processing and disseminating this information. In this paper we develop a theoretical framework which defines the context information necessary for m-commerce applications, taking into account relevant marketing dimensions as well as privacy protection perspectives. Then, this framework is operationalized through the design of an appropriate software architecture which enables the standardization and management of context information.
    Keywords
    Mobile commerce; Consumer behaviour; Innovative services; Context-awareness; Adaptivity; Privacy; Mobile business
  5. [j38]
    Giannikopoulos, P. and Vassilakis, C. A distributed recommender system architecture. In International Journal of Web Engineering and Technology, 7 (3): 203-227, 2012.Abstract & details DOI: 10.1504/ijwet.2012.048517 BibTeX
    Abstract
    In contemporary internet architectures, including server farms and blog aggregators, web log data may be scattered among multiple cooperating peers. In order to perform content personalization through provision of recommendations on such architectures, it is necessary to employ a recommendation algorithm; however the majority of such algorithms are centralized, necessitating excessive data transfers and exhibiting performance issues when the number of users or the volume of data increase. In this paper we propose an approach where the clickstream information is distributed to a number of peers, which cooperate for discovering frequent patterns and for generating recommendations, introducing (a) architectures that allow the distribution of both the content and the clickstream database to the participating peers and (b) algorithms that allow collaborative decisions on the recommendations to the users, in the presence of scattered log information. The proposed approach may be employed in various domains, including digital libraries, social data, server farms and content distribution networks.
    Keywords
    frequent-pattern mining; load balancing; generalised association rule mining; GARM; FP-growth; GP-close; FGP; distributed recommender system
  6. [j37]
    Lykourentzou, I.; Dagka, F.; Papadaki, K.; Lepouras, G. and Vassilakis, C. Wikis in enterprise settings: a survey. In Enterprise Information Systems, 6 (1): 1-53, 2012.Abstract & details Full text DOI: 10.1080/17517575.2011.580008 BibTeX
    Abstract
    The wiki technology is increasingly being used in corporate environments to facilitate a broad range of tasks. This survey examines the use of wikis on a variety of organisational tasks that include the codification of explicit and tacit organisational knowledge and the formulation of corporate communities of practice, as well as more specific processes such as the collaborative information systems development, the interactions of the enterprise with third parties, management activities and organisational response in crisis situations. For each one of the aforementioned corporate functions, the study examines the findings of related research literature to highlight the advantages and concerns raised by the wiki usage and to identify specific solutions addressing them. Finally, based on the above findings, the study discusses various aspects of the wiki usage in the enterprise and identifies trends and future research directions on the field.
    Keywords
    enterprise wikis, corporate wikis, organisational knowledge, wiki research

2011

  1. [j36]
    Antoniou, A.; Diakakis, D.; Lepouras, G. and Vassilakis, C. Towards a methodological framework for the cognitive-behavioural evaluation of educational e-games. In International Journal of Learning Technology, 6 (3): 263-287, 2011.Abstract & details DOI: https://doi.org/10.1504/IJLT.2011.043580 BibTeX
    Abstract
    The proposed methodological framework reviews and uses knowledge from the field of cognitive psychology in order to evaluate aspects of educational games. In particular, we concentrate on two components of human cognition that play a central role to learning, namely memory and motivation. After having reviewed theories in the field, we created a questionnaire in order to evaluate educational games. The questionnaire incorporates different experimental findings of cognitive psychology. Especially, we have applied Maslow’s motivation theory, Behavioural findings on reinforcement, experimental findings about attention and memory. We present the results obtained from the evaluation of two games, PAC-MAN and Mega Jump. The results confirmed the user ratings of the two games, showing that there seem to be cognitive reasons for the success/failure of different games. Finally, lists of guidelines for developers and instructors are included.
    Keywords
    educational games; evaluation methodologies; design guidelines
  2. [j35]
    Vasiliadis, D.; Rizos, G. and Vassilakis, C. Performance Analysis of Multi-Layered Multi-Priority Asymetric-Sized Delta Networks. In Journal of Computer Systems, Networks, and Communications, 2011: 12, 2011.Abstract & details Full text DOI: 10.1155/2011/723102 BibTeX
    Abstract
    In this paper the performance of multi-layered asymmetric-sized finite-buffered Delta Networks supporting multi-class routing traffic is presented and analyzed in the uniform traffic conditions under various loads using simulations. The rationale behind introducing asymmetric-sized buffered systems is to have a better exploitation of available buffer spaces, while the implementation of multi-layered architecture is applied in order to further improve the overall performance of network. The findings of this performance evaluation can be used by network designers for drawing optimal configurations while setting up the network, so as to best meet the performance and cost requirements under the anticipated traffic load and quality of service specifications.
    Keywords
    -
  3. [c74]
    Akim, N. Md.; Dix, A.; Katifori, A.; Lepouras, G.; Shabir, N. and Vassilakis, C. Spreading Activation for Web Scale Reasoning: Promise and Problems. In WebSci 11, poster presentation, pages 1-4, 2011.Abstract & details Full text BibTeX
    Abstract
    Various forms of spreading activation has been used in a number of web systems, not least in the PageRank algorithm. In our own work we have been using this as a technique for managing context over small and large ontologies, and both our own work and that in LarKC suggests that spreading activation has the potential to aid in reasoning over web-scale data sets including the growing set of linked open data resources. Of particular importance is that spreading activation can be applied locally to a dynamic selfselecting working set of an (practically) unbound linked data collection, as well as globally to the entire collection. However, this potential does not come without problems, some concerning the nature of the algorithm on any large data set, and some more to do with the particular nature of linked open data.
    Keywords
    -
  4. [j34]
    Vasiliadis, D. C.; Rizos, G. E. and Vassilakis, C. Performance Analysis of Dual-Priority Multilayer Multistage Interconnection Networks under Multicast Environment. In Journal of Networks, June (6): 858-871, 2011.Abstract & details DOI: https://doi.org/10.4304/jnw.6.6.858-871 BibTeX
    Abstract
    Next-generation network architectures strive to achieve high bandwidth and ultralow latency for the packets traversing the offered end-to-end paths. Multistage Interconnection Networks (MINs) are often employed for implementing NGNs, but while MINs are fairly flexible in handling varieties of traffic loads, they tend to quickly saturate under broadcast and multicast traffic, especially at increasing size networks. As a response to this issue, multilayer MINs have been proposed, however their performance prediction and evaluation has not been studied sufficiently insofar. In this paper, we evaluate and discuss the performance of multilayer MINs under multicast traffic, considering also two levels of packet priorities, since support for multiple QoS levels is an indispensible requirement for NGNs. Different offered loads and buffer size configurations are examined in this context, and performance results are given for the two most important network performance factors, namely packet throughput and delay. We also introduce and calculate a universal performance fac¬tor, which includes the importance aspect of each of the above main performance factors. The findings of this study can be used by NGN system designers in order to predict the performance of each configuration and adjust the design of their communication infrastructure to the traffic requirements at hand.
    Keywords
    performance analysis, multistage interconnection networks, banyan networks, multicast traffic, multilayer networks
  5. [j33]
    Vasiliadis, D. C.; Rizos, G. E.; Vassilakis, C. and Glavas, E. Modelling and performance evaluation of a novel internal priority routing scheme for finite-buffered multistage interconnection networks. In International Journal of Parallel, Emergent and Distributed Systems, 26(5): 381-397, 2011.Abstract & details Full text DOI: 10.1080/17445760.2010.539218 BibTeX
    Abstract
    In this paper, the modelling, analysis and performance evaluation of a novel architecture for internal priority finite-buffered Multistage Interconnection Networks (MINs) is presented. We model the proposed architecture giving the details of its operation and describing its states and detailing conditions and effects of state transition; we also provide a formal model for evaluating its performance. The proposed architecture’s performance is subsequently analyzed under the uniform traffic condition, considering various offered loads, buffer-lengths and MIN sizes, using simulations. We compare the internal priority scheme vs. the non priority (or single priority) scheme, by gathering metrics for the two most important network performance factors, namely packet throughput and the mean time a packet needs to traverse the network. We demonstrate and quantify the improvements on MIN performance stemming from the introduction of priorities in terms of throughput and a combined performance indicator which depicts the overall performance of the MIN. These performance measures can be valuable assets for designers of parallel multiprocessor systems and networks in order to minimize the overall deployment costs and delivering efficient systems.
    Keywords
    multistage interconnection networks, Banyan switches, packet switching, performance analysis, simulation model
  6. [c73]
    Rompa, J.; Lepouras, G.; Vassilakis, C. and Tryfonopoulos, C. OntoFM: A Personal Ontology-based File Manager for the Desktop. In Demo at the 10th International Web Conference, 2011, Bonn, Germany, 2011.Abstract & details Full text BibTeX
    Abstract
    Personal ontologies have been proposed as a means to support the semantic management of user information. Assuming that a personal ontology system is in use, new tools have to be developed at user interface level to exploit the enhanced capabilities offered by the system. In this work, we present an ontology-based file manager that allows semantic searching on the user's personal information space. The file manager exploits the ontology relations to present files associated with specific concepts, proposes new related concepts to users, and helps them explore the information space and locate the required file.
    Keywords
    cs.HC
  7. [c72]
    Benou, P. and Vassilakis, C. A Software Architecture for Provision of Context-Aware Web-based m-Commerce Applications. In Proceedings of the 11th IEEE International Conference on Computer and Information Technology (CIT 2011), IEEE Computer Society, 2011.Abstract & details DOI: 10.1109/CIT.2011.20 BibTeX
    Abstract
    Mobile commerce is gaining significant importance in the recent years as an alternative option of e-commerce for the moving user. The mobile applications through which mcommerce takes place operate in highly dynamic environments with diverse characteristics and under varying conditions. The characteristics and conditions of these environments –called context– should be exploited in order to provide adaptive services; services that offer a suitable user experience and deliver innovative and enhanced capabilities that will facilitate user interaction, attract new customers and maintain existing ones. The goal of adaptivity is realized through the adaptation of user interface, functionality and content of applications using the context information. Therefore, context-awareness constitutes an essential aspect – almost a requirement – of mobile services. In order to realize context-aware services, there is a necessity to capture the context information from its sources, process and distribute it to the software components that will use it. In this paper, we propose a software architecture for context information management suitable for m-commerce applications. We describe the functionality and characteristics of its components, as well as the interaction among these different components
    Keywords
    -
  8. [c71]
    Wallace, M.; Alexopoulos, P.; Papafragkos, I. and Vassilakis, C. Supporting User Roles in Ontology Fuzzification. In Proceedings of the 6th International Workshop on Semantic media adaptation and personalization (SMAP), IEEE Computer Society, 2011.Abstract & details Full text DOI: 10.1109/smap.2011.24 BibTeX
    Abstract
    Manual ontology development is clearly a strenuous task. Whilst a variety of ontological engineering methodologies exist, their actual application is far from trivial, mainly due to the widely diverse nature of the tasks involved. In this work we study these tasks and identify the different types of human experts that are best suited to perform each one. As a result, we present a cooperative version of an ontological engineering methodology, together with a graphical tool that supports it.
    Keywords
    ontology development, domain expert, knowledge engineer, user roles, fuzzification

2010

  1. [j32]
    Katifori, A.; Vassilakis, C. and Dix, A. Ontologies and the brain: Using spreading activation through ontologies to support personal interaction. In Cognitive Systems Research, Volume 11, Issue 1 (1): 25-41, 2010.Abstract & details Full text DOI: 10.1016/j.cogsys.2009.02.001 BibTeX
    Abstract
    Ontologies, as knowledge engineering tools, allow information to be modelled in ways resembling to those used by the human brain, and may be very useful in the context of personal information management (PIM) and task information management (TIM). This work proposes the use of ontologies as a long-term knowledge store for PIM-related information, and the use of spreading activation over ontologies in order to provide context inference to tools that support TIM. Details on the ontology creation and content are provided, along with a full description of the spreading activation algorithm and its preliminary evaluation. Β© 2009 Elsevier B.V.
    Keywords
    Spreading activation; Personal interaction; Ontology; Personal ontology; User tasks
  2. [j31]
    Vasiliadis, D. C.; Rizos, G. E. and Vassilakis, C. Performance Study of Multi-Layered Multistage Interconnection Networks under Hotspot Traffic Conditions. In Journal of Computer Systems, Networks, and Communications, 2010: 11 pages, 2010.Abstract & details Full text DOI: 10.1155/2010/403056 BibTeX
    Abstract
    The performance of Multistage Interconnection Networks (MINs) under hotspot traffic, where some percentage of the traffic is targeted at single nodes, which are also called hot-spots, is of crucial interest. The prioritizing of packets has already been proposed at previous works as alleviation to the tree saturation problem, leading to a scheme that natively supports 2-class priority traffic. In order to prevent hotspot traffic from degrading uniform traffic we expand previous studies by introducing multi-layer Switching Elements (SEs) at last stages in an attempt to balance between MIN performance and cost. In this paper the performance evaluation of dual-priority, double-buffered, multi-layer MINs under single hotspot setups is presented and analyzed using simulation experiments. The findings of this paper can be used by MIN designers to optimally configure their networks
    Keywords
    Multistage interconnection networks, performance evaluation, hotspot traffic, multi-layer networks
  3. [j30]
    Torou, E.; Katifori, A.; Vassilakis, C.; Lepouras, G. and Halatsis, C. Historical research in archives: user methodology and supporting tools. In International Journal on Digital Libraries, 11(1): 25-36, 2010.Abstract & details DOI: 10.1007/s00799-010-0062-4 BibTeX
    Abstract
    Historic research involves finding, using, and correlating informationwithin primary and secondary sources, in order to communicate an understanding of past events. In this process, historians employ their scientific knowledge, experience, and intuition to formulate queries (who was involved in an event, when did an event occur etc.), and subsequently try to locate the pertinent information from their sources. In this article, the authors investigate how historians formulate queries, which query terms are chosen, and how historians proceed in searching for related information in sources. The insight gained from this investigation can be subsequently used for organizing documentswithin historical source repositories and building tools that will enable historians to access the needed informationmore rapidly and fully.
    Keywords
    Historical archives; Tools; Research methodology; Ontology; User study
  4. [j29]
    Vasiliadis, D.C.; Rizos, G.E. and Vassilakis, C. Improving performance of a wireless multimedia traffic-oriented network through prediction of routing. In International Journal on Information Technologies & Security, 2 (3): 3-16, 2010.Abstract & details Full text BibTeX
    Abstract
    Wireless Local Area Networks (WLANs) have developed into a viable technology to support multimedia traffic and are expected to support multimedia services with guaranteed Quality of Service (QoS) for diverse traffic types (video, audio, and data). In this paper, we consider the incorporation of prediction into a generic distance-vector routing protocol for WLANs, evaluate the performance of the resulting routing scheme. Our study considers the enhancement of Distributed Bellman-Ford algorithm, which is a widely used algorithm, and assesses the effectiveness of the enhanced version on top of a fourth generation system (4-G). In order to compare the performance of the standard protocol against that of the prediction-enhanced version, we gather metrics for the two most important network performance factors, namely packet throughput and delay under different mobility and traffic conditions, using the simulation environment of NS-2. Both medium- and high-mobility configurations have been considered in this study.
    Keywords
    Performance Evaluation, Distance Vector Protocol, Routing Information Protocol, Mobile Ad-hoc Networks, Mobility, Multimedia
  5. [j28]
    Benou, P. and Vassilakis, C. The Conceptual Model of Context for Mobile Commerce Applications. In Electronic Commerce Research, Springer-Verlag, 10(2): 139-165, 2010.Abstract & details DOI: 10.1007/s10660-010-9050-4 BibTeX
    Abstract
    Mobile commerce applications adhering to anytime and anywhere paradigm, required to be flexible. They should be able to adapt their interface, services and content towards a certain context. Several proposals for definition of context have been already proposed originating from various areas related to mobile commerce. However, an integrated, formal and methodological approach for the determination and representation of context, adjusted to special characteristics of mobile commerce applications, has not been insofar presented. This is the challenge we address in this paper, through a conceptual model that includes: i) a clear and formal definition of context, ii) the depiction of its specific characteristics as metadata, iii) a methodology for its determination and iv) the presentation of an extension of class diagrams of UML for its representation, all of them tailored to the special nature of mobile commerce applications.
    Keywords
    Mobile commerce; Context; Context-awareness; Adaptation; UML
  6. [j27]
    Dix, A.; Lepouras, G.; Katifori, A.; Vassilakis, C.; Catarci, T.; Poggi, A.; Ioannidis, Y.; Morae, M.; Daradimos, I.; Md.Akima, N.; Humayound, S. R. and Terella, F. From the web of data to a world of action. In Journal of Web Semantics, 8 (4): 394-408, 2010.Abstract & details Full text DOI: 10.1016/j.websem.2010.04.007 BibTeX
    Abstract
    This paper takes as its premise that the web is a place of action, not just information, and that the purpose of global data is to serve human needs. The paper presents several component technologies, which together work towards a vision where many small micro-applications can be threaded together using automated assistance to enable a unified and rich interaction. These technologies include data detector technology to enable any text to become a start point of semantic interaction; annotations for web-based services so that they can link data to potential actions; spreading activation over personal ontologies, to allow modelling of context; algorithms for automatically inferring ‘typing’ of web-form input data based on previous user inputs; and early work on inferring task structures from action traces. Some of these have already been integrated within an experimental web-based (extended) bookmarking tool, Snip!t, and a prototype desktop application On Time, and the paper discusses how the components could be more fully, yet more openly, linked in terms of both architecture and interaction. As well as contributing to the goal of an action and activity-focused web, the work also exposes a number of broader issues, theoretical, practical, social and economic, for the Semantic Web.
    Keywords
    Task support; Spreading activation; Intelligent user interfaces
  7. [j26]
    Dix, A.; Katifori, A.; Lepouras, G.; Vassilakis, C. and Shabir, N. Spreading Activation Over Ontologies: From Personal Context To Web Scale Reasoning. In International Journal of Semantic Computing, 4 (Special issue on Web Scale Reasoning) (01): 59-102, 2010.Abstract & details Full text DOI: 10.1142/S1793351X10000973 BibTeX
    Abstract
    This paper describes methods to allow spreading activation to be used on web-scale information resources. Existing work has shown that spreading activation can be used to model context over small personal ontologies, which can be used to assist in various user activities, for example, in autocompleting web forms. This previous work is extended and methods are developed by which large external repositories, including corporate information and the web, can be linked to the user?s personal ontology and thus allow automated assistance that is able to draw on the entire web of data. The basic idea is augment the personal ontology with cached data from external repositories, where the choice of what data to fetch or discard is related to the level of activation of entities already in the personal ontology or cached data. This relies on the assumption that the working set of highly active entities is relatively small; empirical results are presented, which suggest these assumptions are likely to hold. Implications of the techniques are discussed for user interaction and for the social web. In addition, warm world reasoning is proposed, applying rule-based reasoning over activate entities, potentially merging symbolic and sub-symbolic reasoning over web-scale knowledge bases.
    Keywords
    Personal ontology; spreading activation; web-scale reasoning; context modeling; intelligent user interface; personal information management; warm-world assumption

2009

  1. [c70]
    Torou, E.; Katifori, A.; Vassilakis, C.; Lepouras, G. and Halatsis, C. Capturing the historical research methodology: an experimental approach. In Proceedings of International Conference of Education, Research and Innovation (ICERI 2009), 2009.Abstract & details BibTeX
    Abstract
    This paper presents the results of a study on how historians conduct research in a historical archive, and the methodologies they use while searching. Historic research involves finding, using, interpreting and correlating information within primary and secondary sources, in order to understand past events. The collection of historical data is accomplished through methodical and comprehensive research in primary and secondary sources. An important factor in our study was to understand what kind of data and/or information historians are looking for in a library/historical archive, either printed or digitized, and which research methodologies or research models they use while they investigate a historical archive. Since this issue has not been addressed insofar, and therefore there are no methods for elucidating research methodologies or research models that historians employ / use, we formulated a questionnaire comprising of seven information retrieval tasks commonly addressed in the context of historic research. History researchers were asked to describe in detail how they would proceed in searching for the information they need for completing these tasks. Through this procedure we aimed to investigate the different ways a historian can use to tackle a specific question, examine whether there exists a common research methodology, and the historic researchers? expectations and preferences. The insight gained from this investigation can be used for educational purposes, since it could be useful in the creation / development of a methodology for conducting research on historical information. Furthermore, the findings can be exploited in the context of organizing documents within historical source repositories, so as to facilitate the retrieval of documents by historians; finally the presented findings can serve as a preliminary requirement analysis phase for building tools that will enable historians to access more rapidly and fully the information they need.
    Keywords
    -
  2. [j25]
    Kareliotis, C.; Vassilakis, C.; Rouvas, E. and Georgiadis, P. IQoS-aware exception resolution for BPEL processes: A middleware-based framework and performance evaluation. In International Journal of Web and Grid Services, 5 (3): 284-320, 2009.Abstract & details Full text DOI: 10.1504/IJWGS.2009.028346 BibTeX
    Abstract
    Web Services Business Process Execution Language (WS-BPEL) is widely used nowadays for specifying and executing composite business processes. During the execution, however, of such business processes, a number of faults stemming from the nature of SOA may occur. The WS-BPEL scenario designer must therefore use the provisions offered by WS-BPEL to catch these exceptions and resolve them. The system fault handler specification, however, is an additional task for the WS scenario designer, while the presence of such handlers within the scenario necessitates extra maintenance activities. In this paper, we propose a middleware-based framework for system exception resolution, which undertakes the tasks of failure interception, discovery of alternative services and their invocation. The process of selecting the alternative services can be driven by process consumer-specified Quality of Service (QoS) policy. Moreover, the middleware arranges for bridging syntactic differences between the originally invoked services and functionally equivalent replacements to it, by employing XSLT-based transformations. The middleware is deployed and maintained independently of the WS-BPEL scenarios, thus removing the need for specifying and maintaining system fault handlers within the scenarios. We also present performance measures, establishing that the overhead imposed by the addition of the proposed middleware layer is minimal. Copyright Β© 2009, Inderscience Publishers.
    Keywords
    BPEL process, Exception handling, Exception resolution, Performance metrics, QoS, Ad hoc networks, Middleware, Quality control, Quality of service, Scalability, Web services, Telecommunication services
  3. [c69]
    Golemati, M.; Costas, V.; Katifori, A.; Lepouras, G. and Halatsis, C. Visualizing Hierarchies: Evaluating the Efficiency and Cognitive Effects of Six Visualization Techniques for Browsing and Management Tasks. In Information Visualization 2009, book of abstracts, 2009.Abstract & details BibTeX
    Abstract
    Hierarchical data structures are one of the most commonly used data structures in computer science, and therefore numerous methods and techniques have been proposed for their visualization. In this paper, we present our findings from a user study, in which a number of folder visualization environments were evaluated to assess (a) how efficiently a number of tasks can be performed within the different environments (b) the extent to which using a particular visualization may help the user acquire an accurate cognitive image of the hierarchy structure and its contents and (c) the overall user experience from using a particular visualization environment. The visualization environments considered are representative of major visualization paradigms (zoomable user interfaces, context+focus and space-filling), while both 2D and 3D environments have been included.
    Keywords
    -
  4. [c68]
    Vassilakis, C. and Kareliotis, C. A framework for adaptation in secure web services. In Proceedings of MCIS 2009, 2009.Abstract & details Full text BibTeX
    Abstract
    In the context of service-oriented computing, the introduction of the Quality-of-Service (QoS) aspect leads to the need to adapt the execution of programs to the QoS requirements of the particular execution. This is typically achieved by finding alternate services that are functionally equivalent to the ones originally specified in the program and whose QoS characteristics closely match the requirements, and invoking the alternate services instead of the originally specified ones; the same approach can also be employed for tackling exceptions. The techniques proposed insofar, however, cannot be applied in a secure context, where data are encrypted and signed for the originally intended recipient. In this paper, we introduce a framework for facilitating adaptation in the context of secure SOA.
    Keywords
    Secure web services, Adaptive execution, Quality of Service
  5. [c67]
    Vasiliadis, D.C.; Rizos, G.E. and Vassilakis, C. Routing and performance evaluation of dual priority Delta networks under hotspot environment. In Proceedings - 2009 1st International Conference on Advances in Future Internet, AFIN 2009, pages 24-30, 2009.Abstract & details Full text DOI: 10.1109/AFIN.2009.12 BibTeX
    Abstract
    Large swings in the demand for content are commonplace within the Internet. Although Multistage Interconnection Networks (MINs) are fairly flexible in handling varieties of traffic loads, their performance considerably degrades by hotspot traffic, especially at increasing size networks. As alleviation to the tree saturation problem, the prioritizing of packets is proposed leading to a scheme that natively supports multi priority traffic. In this paper the performance evaluation of double-buffered Delta Networks under single hotspot setups, with different offered loads, and 2-class routing traffic is presented and analyzed using simulation experiments. Performance comparison of dual vs. single priority scheme is outlined under hotspot environment, by calculating a universal performance factor, which effectively includes the importance aspect of each of the two most important performance metrics, namely packet throughput and delay. The findings of this paper can be used by MIN designers to optimally configure their networks. Β© 2009 IEEE.
    Keywords
    Delta networks, Hot spot, Hotspot traffic, Multistage interconnection network, Multistage interconnection networks, Packet throughput, Performance comparison, Performance evaluation, Performance factors, Performance metrics, Priority schemes, Routing traffic, Saturation problems, Simulation, Simulation experiments, Traffic loads, Interconnection networks, Internet, Computer simulation
  6. [c66]
    Vasiliadis, D.C.; Rizos, G.E.; Vassilakis, C. and Glavas, E. Performance evaluation of multicast routing over multilayer multistage interconnection networks. In Proceedings of the 2009 5th Advanced International Conference on Telecommunications, AICT 2009, pages 395-403, 2009.Abstract & details Full text DOI: 10.1109/AICT.2009.72 BibTeX
    Abstract
    Multilayer MINs have emerged mainly due to the increased need for routing capacity in the presence of multicast and broadcast traffic, their performance prediction and evaluation however has not been studied sufficiently insofar. In this paper, we use simulation to evaluate the performance of multilayer MINs with switching elements of different buffer sizes and under different offered loads. The findings of this paper can be used by MIN designers to optimally configure their networks. Β© 2009 IEEE.
    Keywords
    Broadcast traffic, Buffer sizes, Multicast routing, Multicasts, Multistage interconnection network, Performance evaluation, Performance prediction, Switching elements, Interconnection networks, Multicasting, Network routing, Multilayers
  7. [bc8]
    Benou, P. and Vassilakis, C. Exploiting Context in Mobile Applications. In Encyclopedia of Information Science and Technology, Second Edition, pages 1491-1497, IGI Global, 2009.Abstract & details Full text DOI: 10.4018/978-1-60566-026-4.ch236 BibTeX
    Abstract
    In the mobile and pervasive computing environment, software engineering should not treat diversity and mobility as problems to overcome, but seek methods of which it could take advantage instead. In these environments, the selection of purpose-oriented and timely information, tailored to user preferences and media characteristics will ensure an optimised information delivery. To this end, the context .the information that surrounds the human-computer interaction. plays a key role and is rapidly changing in mobile settings, and the understanding of it is indispensable for the application designers in order to choose, capture and exploit it. In this work, we present an architecture facilitating the collection of context information and its exploitation for optimized information delivery, within mobile and pervasive computing environments.
    Keywords
    -
  8. [j24]
    Vassilakis, C.; Lepouras, G. and Katifori, A. A heuristics-based approach to reverse engineering of electronic services. In Information and Software Technology, 51 (2): 325-336, 2009.Abstract & details Full text DOI: 10.1016/j.infsof.2008.04.003 BibTeX
    Abstract
    Since the beginning of the electronic era, public administrations and enterprises have been developing services, through which citizens, businesses and customers can conduct their transactions with the offering entity. Each electronic service contains a substantial amount of knowledge in the form help texts, rules of use or legislation excerpts, examples, validation checks, etc. This knowledge has been extracted from domain experts when the services were developed, especially in the phases of analysis and design, and was subsequently translated into software. In the latter format though, knowledge cannot be readily used in organizational processes, such as knowledge sharing and development of new services. In this paper, we present an approach for reverse engineering electronic services in order to create knowledge items of high levels of abstraction, which can be used in knowledge sharing environments as well as in service development platforms. The proposed approach has been implemented and configured to generate artifacts for the SmartGov service development platform. Finally, an evaluation of the proposed approach is presented to assess its efficiency regarding various aspects of the reverse engineering process. Β© 2008 Elsevier B.V. All rights reserved.
    Keywords
    Government data processing, Management, Reengineering, Reverse engineering, Analysis and designs, Domain experts, e-Government, Electronic services, Help texts, In services, Knowledge sharing, Levels of abstractions, New services, Organizational knowledge, Organizational processes, Public administrations, Reverse engineering processes, Service developments, Validation checks, Knowledge engineering
  9. [c65]
    Kareliotis, C.; Vassilakis, C.; Rouvas, E. and Georgiadis, P. QoS-driven adaptation of BPEL scenario execution. In 2009 IEEE International Conference on Web Services, ICWS 2009, pages 271-278, 2009.Abstract & details Full text DOI: 10.1109/ICWS.2009.80 BibTeX
    Abstract
    BPEL/WSBPEL is the predominant approach for combining individual web services into integrated business processes, allowing for the specification of their sequence, control flow and data exchanges. BPEL however does not include mechanisms for considering the invoked services' Quality of Service (QoS) parameters and thus BPEL scenarios can neither tailor their execution to the individual user's needs or adapt to the highly dynamic environment of the WEB, where new services may be deployed, old ones withdrawn or existing ones changing their QoS parameters. Moreover, infrastructure failures in the distributed environment of the web introduce an additional source of failures that must be considered in the context of QoS-aware service execution. In this work we propose a framework for addressing the issues identified above; the framework allows the users to specify the QoS parameters that they require and it undertakes the task of locating and invoking suitable services. Finally, the proposed framework intercepts and resolves faults occurring during service invocation, respecting the QoS restrictions specified by the consumer. Β© 2009 IEEE.
    Keywords
    Adaptive execution, BPEL, Control flows, Data exchange, Distributed environments, Dynamic environments, Infrastructure failures, Integrated business, New services, Performance evaliation, QoS parameters, Quality of Service parameters, Service execution, Service invocation, Quality of service, Web services

2008

  1. [c64]
    Daradimos, I.; Vassilakis, C. and Katifori, A. A Drupal CMS Module for Managing Museum Collections. In International Symposium on Information & communication technologies in cultural heritage, 2008.Abstract & details BibTeX
    Abstract
    Digitization efforts and web presentations are currently on-going in many museums, archives, libraries and culture heritage institutions in general, exploiting the advent of WWW and digitization technologies. The main benefits from these efforts are exhibit cataloguing, their effective management, preservation and showcasing, and their presentation to the public through the WWW. However, many museums, especially the smaller ones, cannot afford a commercial product and resort to using simple static web pages for their web presence and exhibit presentation. Content Management Systems (CMS), especially open-source ones which come with practically zero-cost, are more and more frequently adopted by museums to create and maintain their website, since they simplify the creation and editing of the web pages and may be used by non-computer experts. In this work we present a module for the Drupal CMS, which provides functionality for (a) Database schema extension to accommodate museum exhibit and collection information (b) Digital exhibit representation (DER) management. (c) Provision of administration pages through which the museum personnel may enter and manage exhibit and collection information (d) WWW scowcasing and (e) Batch data import/export, to facilitate information exchange with other museums.
    Keywords
    -
  2. [c63]
    Katifori, A. and Vassilakis, C. Ontologies as Tools for Historians. In International Symposium on Information & communication technologies in cultural heritage, 2008.Abstract & details BibTeX
    Abstract
    Ontologies have been proven invaluable tools in areas like the semantic web and personal information management. There have been many research efforts to create ontologies and supporting tools for Natural Sciences and Biology in particular (e.g. the GO (http://www.geneontology.org/) ontology and supporting tools). However, the domain of History, the science of studying, recording and organizing the knowledge of the past, has yet to benefit from adopting ontologies. In this work, we present our findings in this area, focusing on the aspects of ontology modeling and ontology visualization.
    Keywords
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  3. [c62]
    Kareliotis, C.; Vassilakis, C.; Rouvas, E. and Georgiadis, P. Exception resolution for BPEL processes: A middleware-based framework and performance evaluation. In Proceedings of the 10th International Conference on Information Integration and Web-based Applications and Services, iiWAS 2008, pages 248-256, 2008.Abstract & details Full text DOI: 10.1145/1497308.1497355 BibTeX
    Abstract
    WS-BPEL is widely used nowadays for specifying and executing composite business processes within the Service Oriented Architecture (SOA). During the execution however, of such business processes, a number of faults stemming from the nature of SOA (e.g. network or server failures) may occur. The WS-BPEL scenario designer must therefore use the provisions offered by WS-BPEL to catch these exceptions and resolve them, usually by invoking some equivalent web service that is expected to be reachable and available. System fault handler specification is though an additional task for the WS scenario designer, while the presence of such handlers within the scenario necessitates extra maintenance activities, as new alternate services emerge or some of the specified ones are withdrawn. In this paper, we propose a middleware-based framework for system exception resolution, which undertakes the tasks of failure interception, discovery of alternate services and their invocation. The middleware is deployed and maintained independently of the WS-BPEL scenarios, removing thus the need for specifying and maintaining system fault handlers within the scenarios. We also present performance measures, establishing that the overhead imposed by the addition of the proposed middleware layer is minimal. Β© 2008 ACM.
    Keywords
    Business Process, Exception handling, Maintenance activity, Middleware layer, Performance evaluation, Performance measure, Performance metrics, Quality of service (QoS), System faults, WS-BPEL, Ad hoc networks, Information retrieval, Information services, Middleware, Quality control, Quality of service, Scalability, Service oriented architecture (SOA), Web services, Telecommunication services
  4. [j23]
    Lepouras, G.; Vassilakis, C.; Sotiropoulou, A.; Theotokis, D. and Katifori, A. An active blackboard for service discovery, composition and execution. In International Journal of Electronic Governance, 1 (3): 275-295, 2008.Abstract & details DOI: 10.1504/IJEG.2008.020450 BibTeX
    Abstract
    Organisations are turning to customer-centric electronic services, oriented to servicing customers' life-events. This development requires methods for automatically locating and synthesising individual services to compose complex ones that will service the customer's life-events, since manual composition, either at the customer or the organisation side, incurs functional, economic and technical problems. In this paper we present an active blackboard architecture, which automates the task of service composition based on the semantics of individual services and data dependencies between them. The blackboard incorporates registries, which facilitate service discovery and an execution engine that arranges for dynamic service composition and execution.
    Keywords
    e-government, electronic services, e-services, service composition, blackboard architecture, semantics, ontologies, electronic governance
  5. [j22]
    Vassilakis, C.; Katifori, A.; Daradimos, E. and Lepouras, G. An Integrated Environment for Cataloguing and Online Presentation of Museum Exhibits. In DESIDOC Journal of Library and Information Technology, 28(4): 72-78, 2008.Abstract & details Full text BibTeX
    Abstract
    The paper presents an integrated environment which enables museum personnel to catalogue and at the same time publish online museum exhibits. The system is based on international standards and is highly customisable to cater the needs of a variety of museum types. Moreover, the underlying database allows storing for the same exhibit documentations for different audiences and in multiple languages, while it is extendable to accommodate new media types, languages, exhibits and information categories. The administrative part of the environment permits the restriction of certain functions to specific personnel roles, enforcing thus a general museum security policy regarding access to and modification of information. The environment presented is currently in use at the Athens University History Museum.
    Keywords
    Museum, online museum exhibits, integrated environment, cataloguing
  6. [c61]
    Mateevitsi, V.; Sfakianos, M.; Lepouras, G. and Vassilakis, C. A game-engine based virtual museum authoring and presentation system. In Proceedings - 3rd International Conference on Digital Interactive Media in Entertainment and Arts, DIMEA 2008, pages 451-457, 2008.Abstract & details Full text DOI: 10.1145/1413634.1413714 BibTeX
    Abstract
    In this paper we present a system that facilitates virtual museum development and usage. The system is based on a game engine, ensuring thus minimal cost and good performance, and includes provisions that enable museum curators design the virtual museum without any specialized knowledge. Besides visual and auditory information, museum curators may also provide metadata which provide additional information to the visitor, while they can be also exploited for searching for exhibits with certain properties. A guide is also included in the museum, to present additional information to the visitors and aid them throughout their tour. Copyright 2008 ACM.
    Keywords
    Metadata, Authoring environment, Game engines, Minimal costs, Museum guide, Presentation systems, Specialized knowledge, Virtual museum, Game theory
  7. [c60]
    Vasiliadis, D.C.; Rizos, G.E.; Vassilakis, C. and Glavas, E. Routing and performance analysis of double-buffered omega networks supporting multi-class priority traffic. In Proc. - The 3rd Int. Conf. Systems and Networks Communications, ICSNC 2008 - Includes I-CENTRIC 2008: Int. Conf. Advances in Human-Oriented and Personalized Mechanisms, Technologies, and Services, pages 56-63, 2008.Abstract & details Full text DOI: 10.1109/ICSNC.2008.10 BibTeX
    Abstract
    In this paper the modeling of Omega Networks supporting multi-class routing traffic is presented and their performance is analyzed. We compare the performance of multi-class priority mechanism against the single priority one, by gathering metrics for the two most important network performance factors, namely packet throughput and delay under uniform traffic conditions and various offered loads, using simulations. Moreover, two different test-bed setups were used in order to investigate and analyze the performance of all priority-class traffic, under different Quality of Service (QoS) configurations. In the considered environment, Switching Elements (SEs) that natively support multi-class priority routing traffic are used for constructing the MIN, while we also consider double-buffered SEs, two configuration parameters that have not been addressed insofar. The rationale behind introducing a multiple-priority scheme is to provide different QoS guarantees to traffic from different applications, which is a highly desired feature for many IP network operators, and particularly for enterprise networks. Β© 2008 IEEE.
    Keywords
    Metropolitan area networks, Quality of service, Systems engineering, Configuration parameters, Enterprise networks, Ip networks, Network performances, Packet throughputs, Performance analyses, Priority schemes, Qos guarantees, Routing traffics, Set-ups, Uniform traffics, Computer networks
  8. [c59]
    Vasiliadis, D. C.; Rizos, G. E. and Vassilakis, C. Evaluation Study of a Wireless Multimedia Traffic-Oriented Network Model. In INTERNATIONAL ELECTRONIC CONFERENCE ON COMPUTER SCIENCE. AIP Conference Proceedings, Volume 1060, pages 379-384, 2008.Abstract & details DOI: 10.1063/1.3037098 BibTeX
    Abstract
    In this paper, a wireless multimedia traffic-oriented network scheme over a fourth generation system (4-G) is presented and analyzed. We conducted an extensive evaluation study for various mobility configurations in order to incorporate the behavior of the IEEE 802.11b standard over a test-bed wireless multimedia network model. In this context, the Quality of Services (QoS) over this network is vital for providing a reliable high-bandwidth platform for data-intensive sources like video streaming. Therefore, the main issues concerned in terms of QoS were the metrics for bandwidth of both dropped and lost packets and their mean packet delay under various traffic conditions. Finally, we used a generic distance-vector routing protocol which was based on an implementation of Distributed Bellman-Ford algorithm. The performance of the test-bed network model has been evaluated by using the simulation environment of NS-2.
    Keywords
    -
  9. [c58]
    Katifori, A.; Torou, E.; Vassilakis, C. and Halatsis, C. Supporting research in historical archives: Historical information visualization and modeling requirements. In Proceedings of the International Conference on Information Visualisation, pages 32-37, 2008.Abstract & details Full text DOI: 10.1109/IV.2008.70 BibTeX
    Abstract
    The on-going progress in the area of digital libraries has lead to the beginning of a digitization effort in Historical Archives, as well. The requirements of historical research, which works with histories of entities and incomplete information, create the need for supplementary tools to support users in handling the digitized content. This work is based on a user study of historian information retrieval methods in order to create a set of tools for the context of historical archives, which will facilitate historical data storage, management and visualization. Β© 2008 IEEE.
    Keywords
    Data visualization, Digital libraries, Information analysis, Information retrieval, Information science, Information services, Information systems, Libraries, Search engines, Heuristics, Historical archive, International conferences, Ontology, Visualization, Information management
  10. [c57]
    Golemati, M.; Katifori, A.; Giannopoulou, E.G.; Daradimos, I.; Vassilakis, C.; Lepouras, G. and Halatsis, C. An interview-based user study on the use of visualizations for folder browsing. In Proceedings of the International Conference on Information Visualisation, pages 106-112, 2008.Abstract & details Full text DOI: 10.1109/IV.2008.90 BibTeX
    Abstract
    Hierarchically structured data collections often need to be visualized for the purposes of digital information management and presentation. File browsing, in particular, has an inherent hierarchical structure and plays an important role in the context of Personal Information Management (PIM). A multitude of file browsers are nowadays available, offering different functionalities, while users adopt diverse practices and habits for browsing activities. In this paper, we investigate these aspects to obtain insights into their advantages and disadvantages and suggest solutions in the area of PIM, as well as in other domains employing similar visualization paradigms. The presented study focuses on the two most widespread visualizations used by file browsers, the indented list and zoomable interface paradigms, and assesses their effectiveness for various tasks and contexts, both by exploiting results on existing evaluations on hierarchy visualizations and folder hierarchy visualizations in particular, and by conducting an interviewbased user study. Β© 2008 IEEE.
    Keywords
    Administrative data processing, Information analysis, Information science, Intermodulation, Intermodulation measurement, Management, Management information systems, Telecommunication services, File browser visualization, Indented list visualization, International conferences, User study, Windows explorer, Information management
  11. [c56]
    Daradimos, I.; Katifori, A. and Vassilakis, C. WhereRU: GPS position reporting and a personal ontology as a virtual community utility. In Proceedings of the 2nd International Conference on Research Challenges in Information Science, RCIS 2008, pages 141-146, 2008.Abstract & details Full text DOI: 10.1109/RCIS.2008.4632102 BibTeX
    Abstract
    The recent progress of the World Wide Web has created new needs for information sharing in virtual communities. WhereRU is a multiuser GPS position reporting system that allows users to make their location publicly available as well as associate it with information on places, persons and events that may later also serve as reminders of the their experiences when traveling.
    Keywords
    Communication, Global positioning system, Information science, Internet, Ontology, Virtual reality, World Wide Web, Gps positions, Information sharing, Multiuser, Personal ontologies, Position reporting, Recent progresses, Reporting systems, Virtual communities, Web community, Satellite navigation aids
  12. [c55]
    Katifori, A.; Torou, E.; Vassilakis, C.; Lepouras, G. and Halatsis, C. Selected results of a comparative study of four ontology visualization methods for information retrieval tasks. In Proceedings of the 2nd International Conference on Research Challenges in Information Science, RCIS 2008, pages 133-140, 2008.Abstract & details Full text DOI: 10.1109/RCIS.2008.4632101 BibTeX
    Abstract
    The need for effective ontology visualization for design, management and browsing has arisen as a result of the progress in the areas of Semantic Web and Personal Information Management. There are several ontology visualizations available through existing ontology management tools, but not as many evaluations to determine their advantages and disadvantages and their suitability for various ontologies and user groups. This work presents selected results of an evaluation of four visualization methods in ProtΓ©gΓ©.
    Keywords
    Communication, Information management, Information retrieval, Information science, Information services, Information theory, Management, Management information systems, Semantic Web, Telecommunication services, User interfaces, Visualization, Comparative studies, Ontology managements, Personal Information managements, User groups, Visualization methods, Ontology
  13. [c54]
    Vasiliadis, D.C.; Rizos, G.E. and Vassilakis, C. Improving performance of finite-buffered blocking delta networks with 2-class priority routing through asymmetric-sized buffer queues. In Proceedings - 4th Advanced International Conference on Telecommunications, AICT 2008, pages 23-29, 2008.Abstract & details Full text DOI: 10.1109/AICT.2008.13 BibTeX
    Abstract
    In this paper the performance of asymmetric-sized finite-buffered Delta Networks with 2-class routing traffic is presented and analyzed in the uniform traffic conditions under various loads using simulations. We compare the performance of 2-class priority mechanism against the single priority one, by gathering metrics for the two most important network performance factors, namely packet throughput and delay. We also introduce and calculate a universal performance factor, which includes the importance aspect of each of the above main performance factors. We found that the use of asymmetric-sized buffered systems leads to better exploitation of network capacity, while the increments in delays can be tolerated. The goal of this paper is to help network designers in performance prediction before actual network implementation and in understanding the impact of each parameter factor. Β© 2008 IEEE.
    Keywords
    Delta networks, International conferences, Performance factors, Computer networks
  14. [c53]
    Katifori, A.; Vassilakis, C. and Dix, A. Using Spreading Activation through Ontologies to Support Personal Information Management. In Proceedings of CSKGOI, within IUI 2008, 2008.Abstract & details Full text BibTeX
    Abstract
    Recent research in the domain of Personal Information Management has recognized the need for a paradigm shift towards a more activity-oriented system. Ontologies, as semantic networks with a structure not dissimilar to the one used by the human brain for storing long-term knowledge, may be very useful as the basis of such a system. This work proposes the use of spreading activation over ontologies in order to provide to a task-based system and its associated tools with methods to record semantics related to documents and tasks and to support user context inference.
    Keywords
    -
  15. [c52]
    Katifori, A.; Vassilakis, C.; Daradimos, I.; Lepouras, G.; Ioannidis, Y.; Dix, A.; Poggi, A. and Catarci, T. Personal Ontology Creation and Visualization for a Personal Interaction Management System. In Proceedings of PIM, CHI 2008, 2008.Abstract & details Full text BibTeX
    Abstract
    Ontologies offer a flexible and expressive layer of abstraction, very useful for capturing the semantics of information repositories and facilitating their retrieval either by the user or by the system to support user tasks. This work presents an ontology-based user profiler, in the context of a Personal Interaction Management System (PIMS). The profiler, based on an ontology of the users? domain, enables them to create their personal ontology by initially choosing one of the available template ontologies as a starting point, which they subsequently populate and customize. The profiler employs a web interface which allows users to populate their personal ontology through forms, hiding ontology complexities and peculiarities. Forms are dynamically generated through ontology views, which are specified by ontology designers.
    Keywords
    User profile, ontology, web-based profiler
  16. [c51]
    Vasiliadis, D.C.; Rizos, G.E. and Vassilakis, C. Performance Evaluation of Distance Vector Routing Protocol on a Wireless Circular Model. In Proceedings of the IEEE sponsored International Joint Conference CISSE 2007, pages 323-328, Springer Netherlands, 2008.Abstract & details DOI: 10.1007/978-1-4020-8737-0 BibTeX
    Abstract
    In this paper, a wireless Circular Model over a generic distance-vector routing protocol is presented and analyzed. The performance of this model over the Distance Vector protocol, which is an implementation of Distributed Bellman-Ford algorithm, has been evaluated by using the simulation environment of NS-2. We conducted an extensive evaluation study for various mobility schemes in order to incorporate the behavior of nodes and the routing protocol in a real-life hotspot situation In the test-bed model, while the number of source nodes was allowed to arbitrarily vary, there was exactly one destination node, closely modeling thus real-life situations where a single hotspot/access point exists. Finally, different constant bit rates (CBR) were used in order to estimate the throughput of receiving, dropping rates, the number of lost packets, as well as the average packet delay under various traffic conditions. This study is aimed to help wireless network designers in choosing the best suited routing protocols for their networks, through making explicit performance figures for common network setups.
    Keywords
    -
  17. [j21]
    Vassilakis, C.; Lepouras, G. and Skiadopoulos, S. Mobile and context-aware e-commerce: Issues, challenges and research directions. In Journal of Electronic Commerce in Organizations, 6 (1): i-iv, 2008.Abstract & details Full text BibTeX
    Abstract
    Electronic commerce, nowadays, is trying to extend its target audience and elevate the quality of services offered to end-users. Two important directions towards meeting these goals are the embracement of mobile users, whose number grows following the advent of communication technologies, and the inclusion of context-aware features in the delivered services to improve the efficiency of the dialogues between users and systems. The context taken into account may involve characteristics regarding the human user, the geographical location and the time of access, the devices employed to access the service, the network through which the user communicates with the system, the nature of the transaction carried out and so forth. It is clear that the development and successful operation of mobile and context-aware e-commerce introduce new challenges. In order to tackle such challenges, new methodologies, tools, architectures and platforms should be made available to assist analysts, designers, developers and operators in handling the various phases of the Mobile and Context-Aware E-Commerce Services (MCACS) lifecycle.
    Keywords
    -
  18. [bc7]
    Golemati, M.; Vassilakis, C.; Katifori, A.; Lepouras, G. and Halatsis, C. Context and Adaptivity-Driven Visualization Method Selection. In Intelligent User Interfaces, pages 188-204, IGI Global, 2008.Abstract & details DOI: 10.4018/978-1-60566-032-5.ch009 BibTeX
    Abstract
    Novel and intelligent visualization methods are being developed in order to accommodate user searching and browsing tasks, including new and advanced functionalities. Besides, research in the field of user modeling is progressing in order to personalize these visualization systems, according to its users’ individual profiles. However, employing a single visualization system, may not suit best any information seeking activity. In this paper we present a visualization environment, which is based on a visualization library, i.e. is a set of visualization methods, from which the most appropriate one is selected for presenting information to the user. This selection is performed combining information extracted from the context of the user, the system configuration and the data collection. A set of rules inputs such information and assigns a score to all candidate visualization methods. The presented environment additionally monitors user behavior and preferences to adapt the visualization method selection criteria.
    Keywords
    -

2007

  1. [c50]
    Vasiliadis, D.C.; Rizos, G.E. and Vassilakis, C. The role of priority mechanisms on performance metrics of double-buffered switching elements. In AIP Conference Proceedings - ICCMSE 2007, pages 937-942, 2007.Abstract & details Full text DOI: 10.1063/1.2836247 BibTeX
    Abstract
    The main concerns in designing the multistage switching fabrics are speed, throughput, delay and variance of delay for a given bandwidth. The rationale behind using various priority mechanisms is either to offer different quality of service levels to packets or to optimize performance parameters of the network, e.g. minimize internal blocking in the Switching Elements (SEs). We investigated the performance parameters of an enhanced priority (EP) mechanism versus a single priority (SP) one. In the EP scheme, packet priority was computed dynamically and was directly proportional to the transmission queue length of the SE that the packet is currently stored in. Finally, we extended the idea of the priority scheme by proposing a multi-priority (MP) mechanism. In the MP scheme, each SE has two transmission queues per link, with one queue dedicated to high priority packets and the other dedicated to low priority ones. We simulated a multistage network under the uniform traffic condition and concluded that the proposed double-buffered SEs provide higher throughput, and decreased latency. Β© 2007 American Institute of Physics.
    Keywords
    -
  2. [j20]
    Lepouras, G.; Vassilakis, C.; Halatsis, C. and Georgiadis, P. Domain expert user development: The smartgov approach. In Communications of the ACM, 50 (9): 79-83, 2007.Abstract & details Full text DOI: 10.1145/1284621.1284623 BibTeX
    Abstract
    SmartGov project funded by the European Union is a knowledge-based platform that assists pubic-sector employees with suitable expertise to generate online transaction devices by simplifying service development, maintenance, and integration with installed information technology systems. The project delivers intelligent e-forms development and maintenance environment and associated framework for e-government services. SmartGov address various problems faced by the stakeholders while implementing e-services such as limited view of domain experts, lost information, complexity of creating e-forms, and inadequate access. In a SmartGov approach, the implicit knowledge is made explicit in the form of documentation and data validation rules. The central concept of SmartGov is the transaction service element (TSE) that contain metadata and domain knowledge.
    Keywords
    Information services, Information technology, Metadata, Online systems, Project management, Data validation, Documentation, Knowledge based platform, Transaction service element (TSE), Knowledge based systems
  3. [c49]
    Vasiliadis, D.C.; Rizos, G.E.; Vassilakis, C. and Glavas, E. Performance evaluation of two-priority network schema for single-buffered delta networks. In IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC, 2007.Abstract & details Full text DOI: 10.1109/PIMRC.2007.4394153 BibTeX
    Abstract
    In this paper a novel two-priority network schema is presented, and exemplified through its application on singlebuffered Delta Networks in packet switching environments. Network operations considered include conflict resolution and communication strategies. The proposed scheme is evaluated and compared against the single-priority scheme. Performance evaluation was conducted through simulation, due to the complexity of the model, and uniform traffic conditions were considered. Metrics were gathered for the two most important network performance factors, namely packet throughput and the mean time a packet needs to traverse the network. The model can also be uniformly applied to several representative networks providing a basis for fair comparison and the necessary data for network designers to select optimal values for network operation parameters. Β© 2007 IEEE.
    Keywords
    Computer simulation, Packet switching, Telecommunication networks, Telecommunication traffic, Network operations, Single-buffered delta networks, Mobile radio systems
  4. [c48]
    Kareliotis, C.; Vassilakis, C. and Georgiadis, P. Enhancing BPEL scenarios with Dynamic Relevance-Based Exception Handling. In ICWS, pages 751-758, 2007.Abstract & details DOI: 10.1109/ICWS.2007.86 BibTeX
    Abstract
    Web services have become the key technology in business processes management. Business processes can be self-contained or be composed from sub-processes; the latter category is typically specified using the Web Services Business Process Execution Language (WS-BPEL) and executed by a Web Services Orchestrator (WSO). During the execution however of such a composite service, a number of faults stemming from the distributed nature of the SOA architecture, e.g. network or server failures may occur. WS-BPEL includes provisions for exception handling, which can be exploited for detecting such failures; once detected, a failure can be resolved by invoking alternate web service implementations that perform the same business task as the failed one. However, the inclusion of such provisions is a tedious assignment for the business process designer, while additional effort would be required to maintain the BPEL scenarios in cases that some alternate WS implementations cease to exist or new ones are introduced. In our research we are developing a framework for automating handling of that kind of exceptions. The proposed solution employs a pre-processor that enhances BPEL scenarios with code that detects failures, discovers alternate WS implementations and invokes them, fully thus resolving the exception. Alternate WS implementation discovery is based on service relevance, which takes into account both functional and qualitative properties of web services.
    Keywords
    -
  5. [c47]
    Golemati, M.; Katifori, A.; Giannopoulou, E.G.; Daradimos, I. and Vassilakis, C. Evaluating the significance of the windows explorer visualization in personal information management browsing tasks. In Proceedings of the International Conference on Information Visualisation, pages 93-98, 2007.Abstract & details Full text DOI: 10.1109/IV.2007.46 BibTeX
    Abstract
    The visualization of hierarchies is very important for digital information management and presentation systems. Especially in the context of Personal Information Management, file browsers play a very important role. Currently the most common file browser visualizations are Windows Explorer and the simple zoomable visualization offered by Microsoft Windows. This work explores the issue of file browser visualization through a user study based on inter-views and an experiment. Β© 2007 IEEE.
    Keywords
    Data reduction, Hierarchical systems, Web browsers, File browser visualization, Indented list visualization, User study, Windows explorer, Information analysis
  6. [c46]
    Vasiliadis, D. C.; Rizos, G. E. and Vassilakis, C. Performance Analysis of dual priority single-buffered blocking Multistage Interconnection Networks. In 3rd International Conference on Networking and Services, ICNS 2007, IEEE, 2007.Abstract & details Full text DOI: 10.1109/ICNS.2007.92 BibTeX
    Abstract
    In this paper a novel architecture of dual priority single-buffered blocking Multistage Interconnection Networks (MINs) is presented. We analyzed their performance in the uniform traffic condition under various loads using simulations. We compared the dual priority architecture against a single priority MIN, by gathering metrics for the two most important network performance factors, namely packet throughput and the mean time a packet needs to traverse the network. We demonstrated the gain of the high priority packets against the low priority packets under different configuration schemas. In this paper we focus on studying the influence of the priority bit in the header field of transmitted packets on the performance of high and low priority traffic of a MIN. Performance prediction before actual network implementation and understanding the impact of parameter settings in a MIN setup are valuable assets for network designers for minimizing overall deployment costs and delivering efficient networks. Β© 2007 IEEE.
    Keywords
    Computer architecture, Interconnection networks, Parameter estimation, Systems engineering, Telecommunication, Telecommunication networks, International conferences, Low priority (LP), Metrics (CO), Multistage interconnection networks Multistage interconnection netowrk (MIN), Network designers, Network performances, Novel architecture, Packet throughput, Parameter settings, Performance analyses, Performance predictions, Schemas, Uniform traffic, Network architecture
  7. [c45]
    Katifori, A.; Golemati, M.; Vassilakis, C.; Lepouras, G. and Halatsis, C. Creating an Ontology for the User Profile: Method and Applications. In RCIS, pages 407-412, 2007.Abstract & details Full text BibTeX
    Abstract
    User profiling is commonly employed nowadays to enhance usability as well as to support personalization, adaptivity and other user-centric features. Insofar, application designers model user profiles mainly in an ad-hoc manner, hindering thus application interoperability at the user profile level, increasing the amount of work to be done and the possibility of errors or omissions in the profile model. This work aims at creating a user profile ontology that incorporates concepts and properties used to model the user profile. Existing literature, applications and ontologies related to the domain of user context and profiling have been taken into account in order to create a general, comprehensive and extensible user model. This ontology can be used as a reference model, in order to alleviate the aforementioned issues. The model, available for download, is exemplified through its application in two different areas, personal information management and adaptive visualization.
    Keywords
    user profile, ontology, user modeling, context
  8. [c44]
    Katifori, A.; Vassilakis, C.; Torou, E.; Lepouras, G.; Halatsis, C. and Daradimos, I. Historical Archive Ontologies Requirements, Modeling and Visualization. In RCIS, pages 401-406, 2007.Abstract & details Full text BibTeX
    Abstract
    Most ontology development methodologies and tools for ontology management deal with ontology snapshots, i.e. they model and manage only the most recent version of ontologies, which is inadequate for contexts where the history of the ontology is of interest, such as historical archives. This work presents a set of requirements for the modeling and visualization of a temporal ontology used as a tool for the representation of historical information. In accordance to these requirements, a visualization plug-in was designed and implemented, featuring a set of tools that enable users to efficiently examine ontology temporal characteristics such as class and instance evolution along the timeline.
    Keywords
    ontology, time, visualization method, entity timeline
  9. [j19]
    Katifori, A.; Halatsis, C.; Lepouras, G.; Vassilakis, C. and Giannopoulou, E. Ontology visualization methods - A survey. In ACM Computing Surveys, 39 (4): 10:1-10:43, 2007.Abstract & details Full text DOI: 10.1145/1287620.1287621 BibTeX
    Abstract
    Ontologies, as sets of concepts and their interrelations in a specific domain, have proven to be a useful tool in the areas of digital libraries, the semantic web, and personalized information management. As a result, there is a growing need for effective ontology visualization for design, management and browsing. There exist several ontology visualization methods and also a number of techniques used in other contexts that could be adapted for ontology representation. The purpose of this article is to present these techniques and categorize their characteristics and features in order to assist method selection and promote future research in the area of ontology visualization. Β© 2007 ACM.
    Keywords
    Digital libraries, Human computer interaction, Information management, Semantic Web, Ontology representation, Ontology visualization, Personalized information management, Visualization methods, Ontology
  10. [c43]
    Kalikakis, M.; Gouscos, D.; Vassilakis, C. and Georgiadis, P. An Approach for re-engineering the Taxation Process to Support Participatory Decisions on Tax Budget Allocation. In Proceedings of the 1st International Conference on Methodologies, Technologies and Tools enabling e-Government, 2007.Abstract & details BibTeX
    Abstract
    The tax collection process has been described as a bureaucratic one, that confines citizen involvement to the role of passive fulfillment of administrative and financial obligations. Active citizen participation, in the form of some political say on the allocation of collected taxes which could potentially improve and further legitimize tax collection, is not a part of the traditional taxation model. In this paper we describe a new taxation model which, in the spirit of participatory budgeting approaches, supports active citizens? participation on decision making regarding tax funds allocation.
    Keywords
    -
  11. [c42]
    Kalikakis, M.; Gouscos, D.; Vassilakis, K. and Georgiadis, P. Towards a P2P world: peered taxation. In Proceedings of the 2nd International Workshop "E-taxation: State & Perspectives", 2007.Abstract & details Full text BibTeX
    Abstract
    This paper presents the current model for taxation and distribution of the taxes to government activities, and an alternative model is presented, according to which tax-payers can determine, to some extent, the way that the taxes they pay will be spent. The goal of this proposal is to increase citizen involvment and system transparency. The model proposal comescomplete with an architecture that supports the realization of the proposed scheme
    Keywords
    Peer-to-Peer, Client-Server, Taxation, Participation
  12. [j18]
    Vassilakis, C.; Lepouras, G. and Halatsis, C. A knowledge-based approach for developing multi-channel e-government services. In Electronic Commerce Research and Applications, 6 (1): 113-124, 2007.Abstract & details Full text DOI: 10.1016/j.elerap.2006.07.004 BibTeX
    Abstract
    Having realised the benefits resulting from delivering on-line public services in the context of electronic government, administrations strive to extend the spectrum of services offered to citizens and enterprises, as well as to engage multiple communication channels in service delivery, in order to increase the target audience and, consequently, the service effectiveness. Insofar, however, only the web channel has been sufficiently used for service delivery, whereas other channels have not been adequately exploited. One of the main reasons of this lag is the cost incurred for the development and maintenance of multiple versions of an electronic service, each version targeted to a different platform. In this paper, we present an approach and the associated tools for developing and maintaining electronic services that allows the automated production of different versions of the electronic service, each targeted to a specific platform. Β© 2006 Elsevier B.V. All rights reserved.
    Keywords
    Communication channels (information theory), Electronic commerce, Knowledge based systems, Online systems, Websites, E-Government, Electronic services, EServices, Multi channel service delivery, Government data processing
  13. [c41]
    Vassilakis, C.; Lepouras, G. and Katifori, A. Web service execution streamlining. In Proceedings - ICSSSM'06: 2006 International Conference on Service Systems and Service Management, pages 1564-1569, 2007.Abstract & details Full text DOI: 10.1109/ICSSSM.2006.320769 BibTeX
    Abstract
    Web services are functional, independent components that can be called over the web to perform a task. Besides being used individually to deliver some well-specified functionality, web services may be used as building blocks that can be combined to implement a more complex function. In such compositions, typically some web services produce results that are used as input for web services that will be subsequently invoked. In the execution schemes currently employed, web services producing intermediate results deliver them to some "coordinating entity", which arranges the forwarding of these intermediate results to web services that require them as input. In this paper we present an execution scheme that employs direct communication between producers and consumers of intermediate results. Besides performance improvement stemming from reduction of network communication, this scheme permits consumer web services to employ simpler authenticity and integrity verification algorithms on incoming parameters. when the producer web service is considered trustworthy. Β©2006 IEEE.
    Keywords
    Algorithms, Function evaluation, Optimization, Parameter estimation, Streamlining, Web service execution, Web service synthesis, Web services
  14. [bc6]
    Vassilakis, C. and Lepouras, G. The Lifecycle of Transactional Services. In Encyclopedia of Digital Government, pages 1174-1179, IGI Global, 2007.Abstract & details DOI: 10.4018/978-1-59140-789-8.ch177 BibTeX
    Abstract
    Transactional services are an indispensible part of e-government, since provision of services to citizens and enterprises,as well as the interaction between the government and citizens-enterprises are modelled mainly through such services. Latest quantifications, however, show that the development of such services lags behind as compared both to the expectations of citizens-enterprises and to the efforts made by governments. This can be attributed, amongst other reasons, to the "traditional" approach to electronic service development, which treats each electronic service as an isolated software project. In this paper, we propose an e-service development platform, which covers the whole lifecycle of transactional services and facilitates the analysis, development, deployment and maintenance of these services.
    Keywords
    -
  15. [bc5]
    Lepouras, G. and Vassilakis, C. Reusability in Governmental Electronic Services. In Encyclopedia of Digital Government, pages 1413-1417, IGI Global, 2007.Abstract & details DOI: 10.4018/978-1-59140-789-8.ch216 BibTeX
    Abstract
    Reusability is the degree to which a software component or other work can be used in more than one programs or software systems. e-Government is a prosperous area for the application of reusability, since the services offered to citizens from the same administration, or even different administrations, have common portions that can be developed only once and reused wherever appropriate. In this paper we present the design and implementation of an electronic service development environment which offers the potential to reuse components that have already been implemented, for the realization of new services.
    Keywords
    -

2006

  1. [c40]
    Vasiliadis, D.C.; Rizos, G.E. and Vassilakis, C. Performance Analysis of Multistage Interconnection Networks determining optimal parameters for data-intensive business applications. In Proceedings of the 7th IBIMA Conference, 2006.Abstract & details BibTeX
    Abstract
    Multistage Interconnection Networks (MINs) are frequently used for connecting processors in parallel computing systems or constructing high speed networks such as ATM (based on Asynchronous Transfer Mode) and Gigabit Ethernet Switches. New applications require distributed computing implementations, but old networks are too slow to allow efficient use of remote resources. Moreover, multimedia are considered as applications with high bandwidth requirements. Some of them are also sensitive to packet loss and claim reliable data transmission. Specific applications require bulk data transfers for database replication or load balancing and therefore packet loss minimization is necessary in order to increase the performance of them. The demand for high performance multimedia services such as full motion video on demand is becoming an increasingly important driving force in the communication market in the Digital Age. Thus, the performance of MINs is a crucial factor, which we have to take into account in the design of new applications. Their performance is mainly determined by their communication throughput and cell latency, which have to be investigated either by time-consuming simulations or approximated by mathematical models. In this paper we investigate the performance of MINs in order to determine optimal values for hardware parameters under diferent operating conditions.
    Keywords
    -
  2. [j17]
    Magoulas, G. D.; Lepouras, G. and Vassilakis, C. Virtual reality in the e-Society. In Virtual Reality, 11 (2-3): 71-73, 2006.Abstract & details Full text DOI: 10.1007/s10055-006-0064-0 BibTeX
    Abstract
    This special issue explores the extent to which virtual reality (VR) is affecting the creation of an electronic society. E-Society is a broad term used to describe a research area covering aspects of digital technologies for large user communities. Recent years have seen the emergence of various electronic services in an attempt to facilitate everyday life and improve the way common tasks are being carried out. The term e-Society covers a wide range of applications from e-government, e-democracy, and e-business to e-learning and e-health. In order for VR to contribute to the creation and advancement of e-Society, a number of issues have to be tackled. A successful VR system has to find a balance between the hardware requirements, user interaction methods, content presentation and the effort required for development and maintenance. Hardware requirements define to a large degree the extent to which an end-user can afford to execute the VR system at her home. User interaction methods have to cater for the variety of users? needs. Overall, design and implementation of a successful and engaging VR system is a rather difficult and complex task which requires increased effort in human power and resources in comparison to typical window based applications. Flexibility in development and subsequently maintenance of such a system can be achieved by adopting techniques already present in rapid application development environments, like abstraction, automatic code generation and reusability.
    Keywords
    Virtual Reality; Virtual Learning Environment; Virtual Reality Technology; Game Engine; Typical Window
  3. [c39]
    Vasiliadis, D.C.; Rizos, G.E. and Vassilakis, C. Performance analysis of blocking banyan switches. In Proceedings of the IEEE sponsored International Joint Conference on Computer, Information and System Sciences and Engineering - CIS2E 06, pages 107-111, Springer Netherlands, 2006.Abstract & details DOI: 10.1007/978-1-4020-6266-7_20 BibTeX
    Abstract
    Banyan Networks are a major class of Multistage Interconnection Networks (MINs). They have been widely used as efficient interconnection structures for parallel computer systems, as well as switching nodes for high-speed communication networks. The performance of them is mainly determined by their communication throughput and their mean packet delay. In this paper we use a model that is based on a universal performance factor, which includes the importance aspect of each of the above main performance factors (throughput and delay) in the design process of a MIN. The model can also uniformly be applied to several representative networks. The complexity of the model requires to be investigated by time-consuming simulations. In this paper we study a typical (8X8) Baseline Banyan Switch that consists of (2X2) Switching Elements (SEs). The objective of this simulation is to determine the optimal buffer size for the MIN stages under different conditions.
    Keywords
    Multistage interconnection networks, baseline networks, delta networks, crossbar switches, packet switching, performance analysis
  4. [c38]
    Kareliotis, C.; Vassilakis, C. and Georgiadis, P. Towards Dynamic, Relevance-Driven Exception Resolution in Composite Web Services. In Proceedings of OOPSLA 2006, Fourth International Workshop on SOA & Web Services Best Practices, 2006.Abstract & details BibTeX
    Abstract
    Web services have become the leading technology for application-toapplication (A2A) communication over distributed and heterogeneous environments. Both academia and industry have strived to enable useful service collaborations among distributed systems without any human intervention. Web service composition can be used to this end, to achieve business automation within one company or realize business-to-business (B2B) integration of heterogeneous software and cross-organizational computing systems. Service composition pro-vides added value, when a web service composition itself becomes a higher level composite web service. However, as business processes are long-lasting transactions, exceptions may often occur, necessitating the replacement of a service component which has been made unavailable, hindering the completion of some business process. In this paper we present an exception resolving approach based on discovering replacement components that are functionally equivalent, taking also into account criteria for qualitative substitutability. The proposed solution introduces the Service Relevance and Replacement Framework (SRRF) which undertakes exception handling.
    Keywords
    -
  5. [c37]
    Torou, E.; Katifori, A.; Vassilakis, C.; Lepouras, G. and Halatsis, C. Creating an Historical Archive Ontology: Guidelines and Evaluation. In ICDIM, pages 102-109, 2006.Abstract & details DOI: 10.1109/ICDIM.2007.369337 BibTeX
    Abstract
    Ontologies have been proven invaluable tools both for the semantic web and for personal information management. In the context of a historical archive an ontology may provide meaningful and efficient support for search tasks as well as be used as a tool for storage and presentation of historical data. The creation however of such an ontology is complex, since the digitized archive documents are not in text format and the concepts that must be captured may vary among different time periods. This work presents a user-centric methodological approach for extracting the ontology of an historical archive focusing on the evaluation issues related to this process. The approach is exemplified through cases from its application in the University of Athens Historical Archive.
    Keywords
    -
  6. [j16]
    Vassilakis, C. and Lepouras, G. Component reuse in electronic services development. In J. Comp. Methods in Sci. and Eng., 6 (5,6 Supplement 2): 229-241, 2006.Abstract & details Full text BibTeX
    Abstract
    In the context of electronic government, e-services are a valuable instrument for offering high quality services to enterprises and individual citizens alike. While developing an e-service, it is usually possible to reuse elements that have already crafted for other e-services, such as personal detail forms or widgets for collecting social security numbers, decreasing thus both development effort and the time for deployment. A more generic framework for supporting reusability in development of e-services includes the identification of reusable objects, the creation and population of a repository containing such components, and the empowerment of developers with tools allowing for location, retrieval and adaptation of components for suiting their specific tasks. In this paper, we conduct an analysis to recognise e-service component that offer reusability opportunities and we present facilities and methods to enable e-service developers to exploit these opportunities while developing electronic services.
    Keywords
    -
  7. [c36]
    Vassilakis, C.; Lepouras, G. and Katifori, A. Reverse engineering electronic services: from e-forms to knowledge. In ICSOFT (1), pages 273-278, 2006.Abstract & details Full text BibTeX
    Abstract
    On their route to e-governance, public administrations have developed e-services. Each e-service encompasses a significant amount of knowledge in the form of examples, help texts, legislation excerpts, validation checks etc. This knowledge has been offered by domain experts in the phases of service analysis, design and implementation, being however bundled within the software, it cannot be readily retrieved and used in other organizational processes, including the development of new services. In this paper, we present an approach for reverse engineering e-services, in order to formulate knowledge items of a high level of abstraction, which can be made available to the employees of the organizations. Moreover, the knowledge items formulated in the reverse engineering process are stored into a knowledge-based e-service development platform, making them readily available for use in the development of other services.
    Keywords
    e-Government, electronic services, reverse engineering, organizational knowledge
  8. [c35]
    Katifori, A.; Torou, E.; Halatsis, C.; Lepouras, G. and Vassilakis, C. A Comparative Study of Four Ontology Visualization Techniques in Protege: Experiment Setup and Preliminary Results. In IV '06: Proceedings of the conference on Information Visualization, pages 417-423, IEEE Computer Society, Washington, DC, USA, 2006.Abstract & details DOI: 10.1109/IV.2006.3 BibTeX
    Abstract
    The continuing need for more effective information retrieval has lead to the creation of the notions of the semantic web and personalized information management, areas of study that very often employ ontologies to represent the semantic context of a domain. Consequently, the need for effective ontology visualization for design, management and browsing has arisen. There are several ontology visualizations available through the existing ontology management tools, but not as many evaluations to determine their advantages and disadvantages and their suitability for various ontologies and user groups. This work presents the preliminary results of an evaluation of four visualization methods in Protege.
    Keywords
    -
  9. [c34]
    Golemati, M.; Halatsis, C.; Vassilakis, C.; Katifori, A. and Lepouras, G. A context-based adaptive visualization environment. In Proceedings of the International Conference on Information Visualisation, pages 62-67, 2006.Abstract & details Full text DOI: 10.1109/IV.2006.5 BibTeX
    Abstract
    Digital libraries and historical archives are increasingly employing visualization systems to facilitate the information retrieval and knowledge extraction tasks of their users. Typically, each organization employs a single visualization system, which may not suit best the needs of certain user groups, specific tasks, or properties of document collections to be visualized. In this paper we present a context-based adaptive visualization environment, which embeds a set of visualization methods into a visualization library, from which the most appropriate one is selected for presenting information to the user. Methods are selected by examining parameters related to the user profile, system configuration and the set of data to be visualized, and employing a set of rules to assess the suitability of each method. The presented environment additionally monitors user behavior and preferences to adapt the visualization method selection criteria. Β© 2006 IEEE.
    Keywords
    Adaptive systems, Behavioral research, Digital libraries, Extraction, Information analysis, Information science, Information services, Information systems, Libraries, Search engines, Solvent extraction, (PL) properties, Adaptive visualization, document collections, Information visualization, Knowledge extraction, Retrieval (MIR), Selection criterion, Set of rules, Specific tasks, System configurations, User behaviors, User groups, user profiling, visualization methods, Visualization systems, Visualization
  10. [c33]
    Katifori, A.; Vassilakis, C.; Lepouras, G.; Daradimos, I. and Halatsis, C. Visualizing a temporally-enhanced ontology. In AVI '06: Proceedings of the working conference on Advanced visual interfaces, pages 488-491, ACM, New York, NY, USA, 2006.Abstract & details DOI: 10.1145/1133265.1133365 BibTeX
    Abstract
    Most ontology development methodologies and tools for ontology management deal with ontology snapshots, i.e. they model and manage only the most recent version of ontologies, which is inadequate for contexts where the history of the ontology is of interest, such as historical archives. This work presents a modeling for entity and relationship timelines in the Prot.g. tool, complemented with a visualization plug-in, which enables users to examine entity evolution along the timeline.
    Keywords
    -
  11. [bc4]
    Lepouras, G.; Sotiropoulou, A.; Theotokis, D. and Vassilakis, C. Tailorable E-Government Information Systems. In Encyclopedia of E-Commerce, E-Government, and Mobile Commerce, pages 1064-1069, IGI Global, 2006.Abstract & details DOI: 10.4018/978-1-59140-799-7.ch171 BibTeX
    Abstract
    Real-world information, knowledge and procedures after which information systems are modeled are generally of dynamic nature and subject to changes, due to the emergence of new requirements or revisions to initial specifications. E-government information systems (eGIS) present a higher degree of volatility in their environment, since requirement changes may stem from multiple sources, including legislation changes, organizational reforms, end-user needs, interoperability and distribution concerns etc. To this end, the design and implementation of eGIS must adhere to paradigms and practices that facilitate the accommodation of changes to the eGIS as they occur in the real world. In this work, we present a role-based model for designing and implementing eGIS that can dynamically accomodate changes, providing the necessary facilities for modeling multiple aspects of the same real-world entities and delivering context-specific behaviour.
    Keywords
    -
  12. [bc3]
    Lepouras, G. and Vassilakis, C. Adaptive Virtual Reality Shopping Malls. In Encyclopedia of E-Commerce, E-Government, and Mobile Commerce, pages 1-6, IGI Global, 2006.Abstract & details DOI: 10.4018/978-1-59140-799-7.ch001 BibTeX
    Abstract
    Firms and organizations are increasingly exploiting electronic channels to reach their customers and create new business opportunities. To this end, electronic shops have been developed, either offering products from a single firm or encompassing multiple individual electronic stores, comprising thus electronic shopping malls. Two main concerns for e-commerce are personalization and enhancement of user experience. Personalization addresses the ability to offer content tailored to the preferences of each user or user group. Preferences may be explicitly declared by the user, or derived by the system through inspecting user interaction; if the system dynamically reacts to changes of visitor behavior, it is termed as adaptive. Enhancement of user experience is another major issue in e-commerce, given that 2D-images and texts on the screen are not sufficient to provide information on products aspects such as physical dimensions, textures and manipulation feedback. Multimedia presentations can also be used as a means for .information acceleration. for promoting "really new" products. This article aims to specify a system that exploits capabilities offered by adaptation and VR technologies to offer e-shoppers personalized and enhanced experiences, while addressing challenges related to the cost, complexity and effort of building and maintaining such a system.
    Keywords
    -
  13. [bc2]
    Vassilakis, C. and Lepouras, G. Ontology for E-Government Public Services. In Encyclopedia of E-Commerce, E-Government, and Mobile Commerce, pages 865-870, Idea Group Inc., 2006.Abstract & details DOI: 10.4018/978-1-59140-799-7.ch139 BibTeX
    Abstract
    In this work, the usage of ontologies for meeting requirements related to e-service composition, e-service cataloguing, change management and administrative responsibility is examined. An ontology for e-government services is presented, covering various aspects of services, including administrative responsibility, meta-data, involved documents and legislation. Both the development and usage phase of the ontology are covered and directions for further exploitation of the potential offered by the ontological representation are given.
    Keywords
    -

2005

  1. [c32]
    Vassilakis, C.; Gouscos, D. and Georgiadis, P. A semantics-based consultations workbench. In ITI 3rd International Conference on Information and Communications Technology, ICICT 2005 - Enabling Technologies for the New Knowledge Society, pages 421-434, 2005.Abstract & details Full text DOI: 10.1109/ITICT.2005.1609641 BibTeX
    Abstract
    Econsultations constitute an effective means to inclusive and informed participation of citizens and society in policy, decision and law formulation processes, and an answer to democratic deficit issues. Econsultation platforms need to support all stages of consultation processes including agenda setting and topics raising, legislation proposal publicity, notification of developments, proposal debate and commentary, collection, analysis and synthesis of views. In this paper we present the design of an open platform assisting policy makers and the civil society in the set-up, enactment, management and federation of inclusive and informed digital consultations. The proposed platform employs semantic techniques, such as semantics, content annotation and summarization to support the consultation processes and provide targeted and digested information to participants, and facilitates tailoring of Econsultation procedures by offering basic Econsultation activities as building blocks, which can be combined according to contextual needs. The platform also enables distinct Econsultation processes to be federated, allowing the exchange of information, which may be subject to different semantic annotations and classifications, according to the rules of each Econsultation process.
    Keywords
    Classification (of information), Data transfer, Decision making, Logic programming, Public policy, Semantics, Content annotation, Econsultations, Platform architecture, Semantic technologies, Knowledge based systems
  2. [c31]
    Vassilakis, C.; Sotiropoulou, A.; Theotokis, D. and Gouscos, D. A Blackboard-oriented Architecture for e-Government service composition. In Proceedings of the IRMA 2005 conference, 2005.Abstract & details Full text BibTeX
    Abstract
    A requirement for electronic government initiatives to succeed is the ability to offer a citizen-centric view of the government model. The most widely adopted paradigm supporting this task is the life event model, which combines basic services offered from multiple public authorities into a single, high-level service that corresponds to an event in a citizen's life. This composition is not always straightforward though, because the constituent services are generally developed in an independent fashion, using incompatible input and output formats; moreover the task of synchronising the documents required and produced by the services is tedious to implement and costly to maintain, since changes to requirements and legislation necessitate continuous updates to this scheme. In this paper, we present a blackboard architecture that can be used to deliver life-event oriented services to the citizens. The blackboard proposed for this architecture is an active one, undertaking the tasks of conversions, where appropriate. The blackboard couples a data flow approach with event-condition-action rules to enable dynamic formulation of life-event services, decentralising their development and maintenance.
    Keywords
    -
  3. [j15]
    Vassilakis, C.; Lepouras, G.; Rouvas, S. and Georgiadis, P. Exploiting form semantics and validation checks to improve e-form layout. In International Journal of Web Engineering and Technology, 2 (1): 81-96, 2005.Abstract & details Full text DOI: 10.1504/IJWET.2005.007465 BibTeX
    Abstract
    On their route to the electronic era, organisations release on the web more and more complex form-based services, which require users to enter numerous data items interrelated by business rules. In such a context, it is crucial to provide optimal form layouts, in order to present the service users with interfaces that facilitate their work. This paper presents an integrated environment, which exploits data item interrelations manifested by the business rules (or validation checks), to optimise the layout of the web forms comprising a complex service. The approach is validated through its application on a tax return form e-service. Copyright Β© 2005 Inderscience Enterprises Ltd.
    Keywords
    Interfaces (computer), Optimization, Taxation, World Wide Web, Electronic services, Form layout, Form semantics, Integrated environment, Usuability, Validation checks, Semantics
  4. [c30]
    Lepouras, G.; Vassilakis, C.; Sotiropoulou, A.; Theotokis, D. and Katifori, A. An active ontology-based blackboard architecture for Web service interoperability. In 2005 International Conference on Services Systems and Services Management, Proceedings of ICSSSM'05, pages 573-578, 2005.Abstract & details Full text DOI: 10.1109/ICSSSM.2005.1499537 BibTeX
    Abstract
    Web services are functional, independent components that can be called over the web to perform a task. Web services are provided by organizations to enable others to perform tasks the organization offers online. However, with an ever increasing number of web services, finding the web service that performs a certain task is not always easy. Furthermore, adopting an end-user point of view what is needed is the actual result and not the service per se. It is often the case that more than one service have to be combined to produce the anticipated outcome, e.g. in the case of life-events. To this end, we propose an active, ontology-based blackboard architecture that aims at tackling the problems inherent in dynamic synthesis of composite web services and at facilitating user interaction with complex e-government transactions. Β© 2005 IEEE.
    Keywords
    Electronic commerce, Interoperability, World Wide Web, Active blackboard architecture, Ontology-based architecture, Web service synthesis, Computer architecture
  5. [j14]
    Vassilakis, C.; Lepouras, G.; Fraser, J. and Haston, S. Barriers To Electronic Service Development. In e-Service Journal, Fall 2005: 41-63, 2005.Abstract & details Full text DOI: 10.2979/esj.2005.4.1.41 BibTeX
    Abstract
    E-government initiatives have been proven to deliver significant benefits, both for suppliers of electronic services (public authorities and organizations) and for the public, to whom services are addressed. However, the pace with which electronic services are made available and adopted is lower than planned or expected; governments tend to be slow in releasing new services, and citizens often prefer to conduct business with the government through paper forms and physical presence, rather than using online methods. This indicates that certain barriers exist that hinder the transition to electronic services. In this paper, we present the results of a survey among electronic service stakeholder groups, to identify the most important barriers to electronic service development. Documentation of barriers is considered important, since administrations may take certain measures to overcome them. Hints on how specific barriers may be overcome are also provided.
    Keywords
    Electronics, Consumer electronics, Questionnaires, Public authorities, Directive interviews, Information technology, Government services, Technology, Electronic structure
  6. [j13]
    Souillard, M.; Souveyet, C.; Vassilakis, C. and Sotiropoulou, A. A flexible framework for managing temporal clinical trial data. In International Journal of Electronic Healthcare, 1 (4): 453-463, 2005.Abstract & details Full text DOI: 10.1504/IJEH.2005.006691 BibTeX
    Abstract
    Clinical trials are processes that produce large volumes of complex data, with inherent temporal requirements, since the state of patients evolves during the trials, and the data acquisition phase itself needs to be monitored. Additionally, since the requirements for all clinical trials have a significant common portion, it is desirable to capture these common requirements in a generalised framework, which will be instantiated for each specific trial by supplementing the trial-specific requirements. In this paper, we present an integral approach to clinical trial management, using a temporal object-oriented methodology to capture and model the requirements, a temporal OODBMS for data storage and a generalised template application, through which trial-specific applications may be generated. Copyright Β© 2005 Inderscience Enterprises Ltd.
    Keywords
    data base, information processing, medical information system, medical research, patient information, quality control, review, telecommunication
  7. [j12]
    Vassilakis, C.; Lepouras, G.; Halatsis, C. and Lobo, T. P. An XML model for electronic services. In Electronic Government, 2 (1): 41-55, 2005.Abstract & details DOI: 10.1504/EG.2005.006647 BibTeX
    Abstract
    With the need for electronic services to be developed and deployed more and more rapidly, it is imperative that concrete models of electronic services are developed, to facilitate systematic work of electronic service stakeholders, concrete semantics and coherent representations across services developed within an organisation. Using the XML language to develop such a model, offers a number of additional advantages, such as rich semantics, facilitation of data interchange, extensibility, high abstraction levels and possibility for mechanical processing. In this paper we present the design aspects of an XML model for electronic services, which has been used for building a repository of interlinked elements representing e-services. A web-based interface for the management of this repository and a tool for automatically compiling e-service descriptions into executable images have been developed alongside. The model has been evaluated by a mixture of electronic service stakeholders, and the results of this evaluation are also presented.
    Keywords
    e-government; electronic service; XML model
  8. [bc1]
    Lepouras, G. and Vassilakis, C. Adaptive Virtual Reality Museums on the Web. In Adaptable and Adaptive Hypermedia Systems, pages 190-205, IGI Global, 2005.Abstract & details DOI: 10.4018/978-1-59140-567-2.ch010 BibTeX
    Abstract
    This chapter presents an architecture for supporting the creation of adaptive virtual reality museums on the web. It argues whether the task of developing adaptive virtual reality museums is a complex one, presenting key challenges, and should thus be facilitated by means of a supporting architecture and relevant tools. The proposed architecture is flexible enough to cater for a variety of user needs, and modular promoting extensibility, maintainability and tailorability. Adoption of this architecture will greatly simplify the development of adaptive virtual reality museums, reducing the needed effort to exhibit digitisation and user profile specification; user profiles are further refined dynamically through the user data recorder and the user modelling engine, which provide input for the virtual environment generator.
    Keywords
    -

2004

  1. [j11]
    Lepouras, G. and Vassilakis, C. Virtual museums for all: Employing game technology for edutainment. In Virtual Reality, 8 (2): 96-106, 2004.Abstract & details Full text DOI: 10.1007/s10055-004-0141-1 BibTeX
    Abstract
    Museums have started to realise the potential of new technologies for the development of edutainment content and services for their visitors. Virtual reality technologies promise to offer a vivid, enjoyable experience to the museums guests, but the cost in time, effort and resources can prove to be overwhelming. In this paper, we propose the use of 3D game technologies for the purpose of developing affordable, easy to use and pleasing virtual environments. To this end, we present a case study based on an already developed version of a virtual museum and a newly implemented version that uses game technologies. The informal assessment indicates that game technologies can offer a prominent and viable solution to the need for affordable desktop virtual reality systems. Β© Springer-Verlag London Limited 2004.
    Keywords
    Virtual museums; Desktop VR; 3D game technologies
  2. [c29]
    Vassilakis, C. and Lepouras, G. Reusability in Electronic Services Development. In Proceedings of the CSITeA 04 conference, 2004.Abstract & details Full text BibTeX
    Abstract
    Electronic government employs electronic services to facilitate interaction with citizens and enterprises and deliver a rich and high quality spectrum of services. Development of electronic services can be greatly assisted, both in terms of development cost and roll-out time, by exploiting the reusability inherent in them. Reusability may be promoted by identifying reusable objects in the context of electronic service development, building and populating a repository with such components and providing the means for developers to locate, extract and adapt them to suit the task at hand. In this paper we analyse electronic services to recognise reusable components and present means and techniques that empower electronic service developers to build electronic services through reusable components.
    Keywords
    -
  3. [j10]
    Maroulis, D.; Aronis, S.; Nassiapoulou, V.; Grammenos, N. and Vassilakis, C. A web browser for ISDN card phones. In Journal of Internet Technology, 5 (3): 267-277, 2004.Abstract & details Full text BibTeX
    Abstract
    In order to cover the ever-increasing need for more direct and easy access to information, new information access means need to be devised or existing ones need to be further exploited. In this paper, we present a mini Web Browser for ISDN card phones, which enables this widespread device to be used for accessing information in the World Wide Web. The implemented web browser supports HTML and WML pages, while special care was taken to tackle the limitations imposed by the ISDN card phone's hardware, such as small screen, limited keyboard, scarce processing and memory resources. One of the techniques employed to increase the capabilities of the ISDN card phone browser was the introduction of a proxy server, which transforms demanding media types to formats that can be handled by the ISDN card phone hardware.
    Keywords
    Bandwidth, Costs, Embedded systems, HTML, Information analysis, Laptop computers, Personal computers, Personal digital assistants, Voice/data communication systems, Integrated multiprotocol, ISDN card phone, Mobile phones, Proxy servers, Web browsers
  4. [j9]
    Lepouras, G.; Katifori, A.; Vassilakis, C. and Charitos, D. Real exhibitions in a virtual museum. In Virtual Reality, 7 (2): 120-128, 2004.Abstract & details Full text DOI: 10.1007/s10055-004-0121-5 BibTeX
    Abstract
    When creating a virtual environment open to the public a number of challenges have to be addressed. The equipment has to be chosen carefully in order to be be able to withstand hard every-day usage, the application has not only to be robust and easy to use, but has also to be appealing to the user, etc. The current paper presents findings gathered from the creation of a multi-thematic virtual museum environment to be offered to visitors of real world museums. A number of design and implementation aspects are described along with an experiment designed to evaluate alternative approaches for implementing the navigation in a virtual museum environment. The paper is concluded with insights gained from the development of the Virtual Museum and portrays future research plans.
    Keywords
    Evaluation; Interaction design; Virtual environment; Virtual museum
  5. [c28]
    Lepouras, G.; Sotiropoulou, A.; Theotokis, D. and Vassilakis, C. Tailorability in the context of E-government Information Systems: An approach. In Proceedings of the IRMA 2004 conference, 2004.Abstract & details Full text BibTeX
    Abstract
    The ever changing environment information systems model, and in particular e-government ones, intensifies the need for systems that are able to easily, efficiently and transparently adapt to changing environments. Accommodating unanticipated changes implies that systems must be able to adapt to changes occurring in and evolve in step with their changing environment. Adaptation is concerned with monitoring, analysing and understanding the patterns of the user's interaction with the system. Similarly, an information system is said to be evolutionary if it can be purposefully used in a dynamic environment. E-government information systems, in virtue of their nature and function, are driven by the need to adapt and evolve. This suggests that the design and implementation of such systems must provide the necessary infrastructure for evolution and adaptability. In other words, e-government information systems must abide to the Tailorable Information Systems paradigm. In this work we present a case study for the development of a Tailorable e-government information system.
    Keywords
    -
  6. [c27]
    Weir, G.R.S.; Lepouras, G. and Vassilakis, C. Content enrichment through dynamic annotation. In ICEIS 2004 - Proceedings of the Sixth International Conference on Enterprise Information Systems, pages 152-157, 2004.Abstract & details Full text BibTeX
    Abstract
    This paper describes a technique for interceding between users and the information that they browse. This facility, that we term 'dynamic annotation', affords a means of editing Web page content 'on-the-fly' between the source Web server and the requesting client. Thereby, we have a generic way of modifying the content displayed to local users by addition, removal or reorganising any information sourced from the World-Wide Web, whether this derives from local or remote pages. For some time, we have been exploring the scope for this device and we believe that it affords many potential worthwhile applications. Here, we describe two varieties of use. The first variety focuses on support for individual users in two contexts (second-language support and second language learning). The second variety of use focuses on support for groups of users. These differing applications have a common goal which is content enrichment of the materials placed before the user. Dynamic annotation provides a potent and flexible means to this end.
    Keywords
    Content based retrieval, Information analysis, Knowledge based systems, Learning systems, Servers, Web browsers, Content enrichment, Dynamic annotation, World Wide Web
  7. [j8]
    Vassilakis, C.; Lepouras, G.; Rouvas, S. and Georgiadis, P. Integrating e-government public transactional services into public authority workflows. In Electronic Government, 1 (1): 49-60, 2004.Abstract & details DOI: 10.1504/EG.2004.004136 BibTeX
    Abstract
    Documents submitted by citizens through electronic services deployed in the context of e-Government must usually undergo processing by some organisational information system, in order to complete the citizens? requests and for the reply to be returned to the citizen. The integration, however, of the e-service delivery platform and the organisational information system is often hindered for a number of reasons, including security considerations, platform diversity or idiosyncrasies of legacy information systems. In this paper we present a generic method for providing seamless communication between the two platforms, enabling the full integration of documents submitted through electronic services into the organisational workflow, leveraging thus the quality of services offered to the citizens and facilitating e-service development and operation.
    Keywords
    electronic services; e-government; integration; communication; security; scheduling

2003

  1. [j7]
    Vassilakis, C.; Laskaridis, G.; Lepouras, G.; Rouvas, S. and Georgiadis, P. A framework for managing the lifecycle of transactional e-government services. In Telematics and Informatics, 20 (4): 315-329, 2003.Abstract & details Full text DOI: 10.1016/S0736-5853(03)00011-X BibTeX
    Abstract
    Filling and submission of electronic forms is a key issue for e-government, since most electronic services offered in this context include some variant of electronic forms. Insofar, IT experts are placed in the centre of electronic forms services lifecycles, undertaking the analysis, design, implementation and maintenance phases. This practice, however, implies various impediments, such as the need for multitudinous teams with diverse skills. In this paper, we present experiences from developing and maintaining a set of electronic services for the Greek Ministry of Finance, and propose an approach to handling electronic services' lifecycle that balances responsibilities between domain experts and IT professionals. This approach enables a more holistic management of the electronic service lifecycle, by employing modelling and representation in high levels of abstraction and incorporating tools for automatically generating operative service instances from these high-level descriptions. Β© 2003 Elsevier Science Ltd. All rights reserved.
    Keywords
    Communication, Information technology, Electronic forms, Information science
  2. [c26]
    Gorilas, S.; Vassilakis, K.; Lobo, T. P. and Tabouris, E. E-forms Services for the Public Sector: Shifting Development Effort from Programmers to Domain Experts. In Proceedings of e-Challenges 2003, 2003.Abstract & details BibTeX
    Abstract
    E-forms have a central role in a significant number of e-government services. This paper presents a knowledge-based technical platform aiming to assist public sector employees to generate online transaction services by simplifying their development, maintenance and integration with installed IT systems. At the heart of this platform lies the knowledge and transaction services repository. This repository consists of a number of XML document types that incorporate all necessary details for creating and managing online transaction services. The main underlying idea is to provide a platform with intuitive interfaces that can be used directly by domain experts thus minimising the need for personnel with IT skills. This platform is currently under development within the IST SmartGov project.
    Keywords
    -
  3. [c25]
    Lepouras, G.; Katifori, A.; Vassilakis, C. and Charissi, A. Facilitating VR Museums Web Presence. In Proceedings of HCI 2003, pages 1143-1147, 2003.Abstract & details Full text BibTeX
    Abstract
    The paper presents an environment that enables museum curators to catalogue and publish on the web exhibits in multiple languages and media including 3D, video, images. The system is extendable to accommodate new media types, languages, exhibits, information categories, etc. Visitors have the potential to formulate dynamic personalised exhibit collections using search mechanisms provided by the system.
    Keywords
    -
  4. [c24]
    Vassilakis, C.; Lepouras, G.; Rouvas, S. and Georgiadis, P. Improving e-Form Layout Through Analysis of Form Semantics and Validation Checks. In CAiSE Short Paper Proceedings, 2003.Abstract & details Full text BibTeX
    Abstract
    Transaction services offered by public authorities vary from simple forms with few fields to multi-form compound documents with hundreds of input areas. In the latter case, field placement within forms is of particular importance for facilitating the filling and error correction processes. In this paper we present an approach to improving the form layout by exploiting validation checks that are usually associated with electronic forms, as well as semantic information that may be attached to form fields by designers.
    Keywords
    -
  5. [j6]
    Lepouras, G.; Vassilakis, C. and Weir, G. R.S. A system to support dissemination of knowledge and sharing of experiences in the working environment: Review Code 066. In International Journal of Continuing Engineering Education and Lifelong Learning, 13 (3/4): 248-257, 2003.Abstract & details Full text DOI: 10.1504/ijceell.2003.003277 BibTeX
    Abstract
    In the information era, enterprises strive to be productive and efficient. One feature of this goal is for employers to engage their employees in education programs, to help them to gain new experiences and knowledge and to adapt to an ever-changing working environment. Such programs must be carefully designed in order to achieve satisfactory results. Recently, enterprises, recognising the role that technology can play in the education of their employees, have adopted systems that supplement the traditional educational model with mechanisms that enable the sharing of experiences and knowledge. In this paper we describe an architecture and a system prototype that allows users to search easily for information, interact with colleagues and share experiences, and to compose and disseminate best practices and knowledge. The design of this system is based on insights gained from the operation of the Greek taxation system.
    Keywords
    Education computing, Engineering education, Information dissemination, Systems analysis, Integrated systems, Knowledge based systems

2002

  1. [c23]
    Gouscos, D.; Rouvas, S.; Vassilakis, C. and Georgiadis, P. An Object-Oriented Approach for Designing Administrative E-forms and Transactional E-services. In OOIS '02: Proceedings of the 8th International Conference on Object-Oriented. Information Systems, pages 19-30, Springer-Verlag, London, UK, 2002.Abstract & details DOI: 10.1007/3-540-46102-7_6 BibTeX
    Abstract
    Although electronic transaction services are considered to be a necessity for e-government, it has not been possible insofar to unleash their full potential. E-forms are central to the development of e-government, being a basic means for implementing the majority of the public services considered as required for local and central public administration authorities. In this paper, we present an object-oriented model for e-form-based administrative services, which spans the e-service lifecycle, including development, deployment and use by enterprises and citizens, data collection and communication with legacy information systems. The proposed approach encompasses semantic, structural and active aspects of e-forms, providing thus an inclusive framework for modelling electronic services.
    Keywords
    -
  2. [c22]
    Vassilakis, C. and Lepouras, G. Controlled Caching of Dynamic WWW Pages. In DEXA '02: Proceedings of the 13th International Conference on Database and Expert Systems Applications, pages 9-18, Springer-Verlag, London, UK, 2002.Abstract & details Full text DOI: 10.1007/3-540-46146-9_2 BibTeX
    Abstract
    Web sites employ dynamically generated pages for content delivery more and more often, in order to increase their flexibility and provide up-to-date information. This practice, however, increases server load dramatically, since each request results to the execution of code, which may involve processing and/or access to information repositories. In this paper we present a scheme for maintaining a server-side cache of dynamically generated pages, allowing for cache consistency maintenance, without placing heavy burdens on application programmers. We also present insights to architecture scalability and some results obtained from conducted experiments.
    Keywords
    -
  3. [c21]
    Vassilakis, C.; Laskaridis, G.; Lepouras, G.; Rouvas, S. and Georgiadis, P. Transactional e-Government Services: An Integrated Approach. In EGOV '02: Proceedings of the First International Conference on Electronic Government, pages 276-279, Springer-Verlag, London, UK, 2002.Abstract & details Full text DOI: 10.1007/978-3-540-46138-8_44 BibTeX
    Abstract
    Although form-based transactional services are fundamental to electronic government activities, their widespread does neither meet the citizen's expectations, nor the potential offered by state-of-the-art technologies. Besides any bureaucratic impediments, the primary reason for this is that traditional software engineering approaches cannot satisfactorily handle all the aspects of electronic services lifecycle. In this paper we present experiences from developing and maintaining a set of electronic services for the Greek Ministry of Finance, and propose a new approach for handling electronic service projects. The proposed approach has been successfully employed for developing extensions to the existing services, as well as some new ones.
    Keywords
    -
  4. [c20]
    Georgiadis, P.; Lepouras, G.; Vassilakis, C.; Boukis, G.; Tambouris, E.; Gorilas, S.; Davenport, E.; Macintosh, A.; Fraser, J. and Lochhead, D. SmartGov: A Knowledge-Based Platform for Transactional Electronic Services. In Lecture Notes in Computer Science, pages 362-369, Springer Berlin Heidelberg, 2002.Abstract & details Full text DOI: 10.1007/978-3-540-46138-8_59 BibTeX
    Abstract
    Public transaction services (such as e-forms) although perceived the future of e-government have not yet realised their full potential. E-forms have a significant role in e-government, as they are the basis for implementing most of the twenty public services that all member states have to provide to their citizens and businesses. The aim of the SmartGov project is to specify, develop, deploy and evaluate a knowledge-based platform to assist public sector employees to generate online transaction services by simplifying their development, maintenance and integration with already installed IT systems. This platform will be evaluated in two European countries (in one Ministry and one Local Authority). This paper outlines key issues in the development of the SmartGov system platform.
    Keywords
    -
  5. [c19]
    Lepouras, G.; Vassilakis, C. and Weir, G. R. S. Serving Enhanced Hypermedia Information. In Proceedings of the 24th BCS-IRSG European Colloquium on IR Research, pages 86-92, Springer-Verlag, London, UK, 2002.Abstract & details DOI: 10.1007/3-540-45886-7_6 BibTeX
    Abstract
    An apparent limitation of existing Web pages is their inability to accommodate differences in the interests and needs of individual users. The present paper describes an approach that dynamically customises the content of public Web-based information via an interceding 'enhancement server'. The design and operation of this system is described with examples drawn from two current versions. Indications from early trials support the view that this approach affords considerable scope for accommodating the needs and interests of individual Web users.
    Keywords
    -
  6. [c18]
    Tambouris, E.; Boukis, G.; Vassilakis, C.; Lepouras, G.; Rouvas, S.; Canadas, R.; Heredia, S. and Lopez Usero, J. C. SMARTGOV: A Governmental Knowledge-based Platform for Public Sector Online Services. In Proceedings KMGov2002, pages 173-185, Copenhagen, Denmark, 2002.Abstract & details Full text BibTeX
    Abstract
    Public transaction services (such as e-forms), although perceived the future of e-government have not yet realised their full potential. E-forms have a significant role in e-government, as they are the basis for realising most of the twenty public services that all European Union member states have to provide to their citizens and businesses. The aim of this paper is to present a knowledge-based platform to assist public sector employees to generate online transaction services by simplifying their development, maintenance and integration with already installed IT systems.
    Keywords
    -

2001

  1. [c17]
    Laskaridis, G.; Vassilakis, C.; Lepouras, G. and Rouvas, Ef. e-Citizens and e-Consumers: Is There a Difference?. In Proceedings of the PCHCI 2001 Workshop: "Transforming Web Surfers to E-Shoppers", pages 47-50, 2001.Abstract & details Full text BibTeX
    Abstract
    Both the business sector and the government are nowadays embracing Internet technologies in order to provide high quality on-line services to their "target groups". In both cases, service providers are trying to transform web surfers, casually visiting their web sites to seek information, to users of their electronic services, i.e. e-consumers and. e-citizens. In this paper, we address the similarities and the differences between the business and the government, when they act as service providers, with respect to the factors for successful service and the issues that must be addressed.
    Keywords
    e-services, .e-shops, citizens, consumers
  2. [c16]
    Lepouras, G.; Charitos, D.; Vassilakis, C.; Charissi, A. and Halatsi, L. Building a VR - Museum in a Museum. In Proceedings of the Third International Virtual Reality Conference, VRIC2001, 2001.Abstract & details Full text BibTeX
    Abstract
    Past years have seen the exploitation of multimedia techniques and lately the introduction of virtual reality methods to create new forms of presentation for museums' exhibitions. Virtual Reality can offer a number of advantages to museums, offering a way to overcome some common problems like the lack of space or the need of visitors to interact with the exhibits. A broad categorisation of virtual museums reveals that they vary from fully immersive cave systems to simple multimedia presentations. In our approach to develop a virtual reality museum we have designed a virtual environment (VE) where guests can visit a total of ten different museums. The processes of digitisation, architectural design and exhibit presentation are outlined and points of particular importance are explained. Exhibits from the real world museums have been digitised and integrated in the VE. The system has been implemented in two versions: one fully immersive and one with a stereo display.
    Keywords
    Virtual Reality, virtual museum, exhibit digitisation, virtual architecture
  3. [c15]
    Charitos, D.; Lepouras, G.; Vassilakis, C.; Katifori, V.; Charissi, A. and Halatsi, L. Designing a virtual museum within a museum. In Proceedings VAST 2001 Virtual Reality, Archeology, and Cultural Heritage, pages 284, 2001.Abstract & details Full text DOI: 10.1145/584993.585043 BibTeX
    Abstract
    The designing of a virtual museum within a museum was discussed. In regard with it, the Virtual Museum project sponsored by the Greek General Secretariat of Research and Technology was presented. The project's main objective was to create a virtual environment (VE) for enhancing the experience of visiting a museum by affording view and manipulation of certain exhibits.
    Keywords
    Information retrieval systems, Internet, Museums, Technical presentations, Three dimensional computer graphics, Virtual museum, Virtual reality

2000

  1. [j5]
    Vassilakis, C. An optimisation scheme for coalesce/valid time selection operator sequences. In SIGMOD Record (ACM Special Interest Group on Management of Data), 29 (1): 38-43, 2000.Abstract & details Full text DOI: 10.1145/344788.344803 BibTeX
    Abstract
    Queries in temporal databases often employ the coalesce operator, either to coalesce results of projections, or data which are not coalesced upon storage. Therefore, the performance and the optimisation schemes utilised for this operator is of major importance for the performance of temporal DBMSs. Insofar, performance studies for various algorithms that implement this operator have been conducted, however, the joint optimisation of the coalesce operator with other algebraic operators that appear in the query execution plan has only received minimal attention. In this paper, we propose a scheme for combining the coalesce operator with selection operators which are applied to the valid time of the tuples produced from a coalescing operation. The proposed scheme aims at reducing the number of tuples that a coalescing operator must process, while at the same time allows the optimiser to exploit temporal indices on the valid time of the data.
    Keywords
    Temporal databases; Coalescing; Valid time selection; Optimisation; Query Processing
  2. [c14]
    Lepouras, G. and Vassilakis, C. Multilingual Web Site Construction and Maintenance. In Proceedings of the SCI 2000 conference, pages 56-61, 2000.Abstract & details BibTeX
    Abstract
    The construction of multilingual web sites is probably the best answer to addressing the problem of the diverse cultural background of the Internet community. However, developing multiple instances of the same site in different languages induces increased overhead for both the implementation and the maintenance phase. The paper reviews current techniques and describes an alternative to constructing multilingual web sites, which eases the development and maintenance phases, without possessing any of the drawbacks of existing tools. The paper concludes proposing possible future enhancements.
    Keywords
    -
  3. [j4]
    Kovacs, L. and Vassilakis, C. Function oriented history representation in databases. In Computers and Artificial Intelligence, 19 (5): 417-444, 2000.Abstract & details Full text BibTeX
    Abstract
    In the past years the management of temporal data has attracted numerous researchers resulting to a large number of temporal data extensions to the relational and object oriented data models. In this paper, the proposed temporal data model focuses on the functional characteristics of the histories. The paper introduces a set oriented description of the calendars together with a function oriented history concept with a history-algebra. The completeness of the proposed model with respect to the reduced temporal algebra TA is also proven. The expressive power of the proposed model is demonstrated in the end of the paper by a hospital example.
    Keywords
    Temporal databases, calendars, history, history algebra
  4. [c13]
    Charitos, D.; Lepouras, G.; Vassilakis, C.; Katifori, V. and Halatsi, L. An Approach to Designing and Implementing Virtual Museums. In Proceedings of the seventh UK VR-SIG Conference, 2000.Abstract & details Full text BibTeX
    Abstract
    The current paper describes an approach to designing and implementing a virtual environment comprising ten different museums. The number of museums as well as the variety of their exhibits lead to the adoption of a generalised strategy that catered for all museum presentation needs and allowed for future expansion. Furthermore, the system architecture supports the delivery of multimedia content either over the Internet or via a local immersive virtual reality installation.
    Keywords
    virtual reality, virtual museum, digital exhibit

1999

  1. [c12]
    Vassilakis, C. and Lepouras, G. Is Server-Side Programming Killing Your Web Server?. In Proceedings of the ActiveWeb 99 Conference, Staffordshire University, 1999.Abstract & details Full text BibTeX
    Abstract
    The paper addresses issues related to client/server technologies and specifically the effectiveness of server-side programming techniques. The motive for this study was the need to create a lightweight and dynamic navigational aid for use in a web site. Towards this goal a number of possible solutions were considered and for two of them an experiment was run to determine the best suited for our case. The rest of the paper outlines our findings.
    Keywords
    -
  2. [c11]
    Theotokis, D.; Kapos, G. D.; Vassilakis, C.; Sotiropoulou, A. and Gyftodimos, G. Distributed Information Systems Tailorability: A Component Approach. In Proceedings 7th IEEE Workshop on Future Trends of Distributed Computing Systems, pages 95, IEEE Comput. Soc, Washington, DC, USA, 1999.Abstract & details DOI: 10.1109/FTDCS.1999.818790 BibTeX
    Abstract
    Distributed software systems need to evolve according to the ever-changing requirements on which they were built. Software systems' tailorability can be achieved in terms of component software. Atoms and molecules the basic constructs of the ATOMA framework are the building blocks for distributed tailorable component-based software systems. These constructs can be considered as independent agents, that communicate in terms of unanticipated, connections that are established at runtime, thus forming agent communities. System tailorability can take place at two levels. In high level tailorability whole parts of the functionality of a system, represented as agents, can be altered in order to provide new functionality. At a lower level, the tailorability of an agent itself that is the tailorability of its functionality, is achieved through a flexible service mapping implementation for rule-based method invocation.
    Keywords
    -

1998

  1. [j3]
    Vassilakis, C.; Lorentzos, N. and Georgiadis, P. Implementation of transaction and concurrency control support in a temporal DBMS. In Information Systems, 23 (5): 335-350, 1998.Abstract & details Full text DOI: 10.1016/S0306-4379(98)00015-5 BibTeX
    Abstract
    Transactions and concurrency control are significant features in database systems, facilitating functions both at user and system level. However, the support of these features in a temporal DBMS has not yet received adequate research attention. In this paper, we describe the techniques developed in order to support transaction and concurrency control in a temporal DBMS that was implemented as an additional layer to a commercial DBMS. The proposed techniques make direct use of the transaction mechanisms of the DBMS. In addition, they overcome a number of limitations such as automatic commit points, lock release and log size increment, which are imposed by the underlying DBMS. Our measurements have shown that the overhead introduced by these techniques is negligible, less than 1% in all cases. The approach undertaken is of general interest, it can also be applied to non-temporal DBMS extensions. Copyright Β© 1998 Elsevier Science Ltd. All rights reserved.
    Keywords
    Concurrency control, Data structures, Temporal databases, Database systems
  2. [c10]
    Vassilakis, C.; Georgiadis, P. and Sellis, T. K. Implementing Embedded Valid Time Query Languages. In DEXA '98: Proceedings of the 9th International Conference on Database and Expert Systems Applications, pages 561-572, Springer-Verlag, London, UK, 1998.Abstract & details DOI: 10.1007/BFb0054514 BibTeX
    Abstract
    Application development on top of database systems is heavily based on the existence of embedded and 4GL languages. However, the issue of designing and implementing embedded or 4GL temporal languages has not been addressed insofar. In this paper, we present a design approach for implementing an embedded temporal language that supports valid time. Furthermore, we introduce implementation techniques that can be used for implementing any embedded temporal language that supports valid time on top of a DBMS.
    Keywords
    -
  3. [c9]
    Souillard, M.; Vassilakis, C. and Sotiropoulou, A. TOOBIS: Application de la gestion de donn'ees temporelles dans le domaine de la recherche clinique. In INFORSID, pages 147-165, 1998.Abstract & details Full text BibTeX
    Abstract
    Les donn?es temporelles, c'est-?-dire des donn?es ?voluant dans le temps et pour lesquelles il est int?ressant de maintenir un historique des valeurs, ne sont pas utilis?es dans l'industrie. Mais cela ne veut pas dire pour autant que les diverses applications existantes ne g?rent que des donn?es non temporelles. En fait, des donn?es temporelles doivent ?tre g?r?es par un grand nombre d'applications et de secteurs industriels tels que la finance, l'assurance, le suivi m?dical, les services de r?servation, etc. Ces applications utilisent le plus souvent le r?sultat de d?veloppements internes simulant des donn?es temporelles, qui peuvent ?tre co?teux. Le march? des solutions pour manipuler des donn?es temporelles est encore limit?, et ne r?pond pas ? tous les besoins. Cet article pr?sente les r?sultats du projet europ?en TOOBIS - Temporal Object Oriented dataBase within Information System - en mettant l'accent sur une application g?rant des donn?es temporelles, d?velopp?e dans le domaine de la Recherche Clinique. TOOBIS propose une extension du standard des bases de donn?es orient?es objet afin de fournir un syst?me de gestion des bases de donn?es temporelles complet, ainsi qu'une m?thodologie de conception temporelle.
    Keywords
    Time, Object, Database, Model, Languages, Clinical Research
  4. [c8]
    Sotiropoulou, A.; Souillard, M. and Vassilakis, C. Temporal Extension to ODMG. In IADT, pages 304-311, 1998.Abstract & details Full text BibTeX
    Abstract
    In the past years a number of temporal extensions to the different database models have been proposed. Extensions to the relational model have been following the different SQL standards, while no attempts have been made to extend the OO-databases’ standard, defined by ODMG. In this paper we present a temporal extension to the ODMG standard, as this has been specified in the TOOBIS project. A Temporal Object Data Model, a Temporal Object Definition Language and a Temporal Object Query Language have been specified and have been proposed as extensions to the ODM, ODL and OQL of ODMG. This extension has been implemented over a commercial OODBMS, reinforcing and validating the effort of standardisation and portability of this extension.
    Keywords
    -

1996

  1. [c7]
    Vassilakis, C.; Georgiadis, P. and Sotiropoulou, A. A comparative study of temporal DBMS architectures. In DEXA '96: Proceedings of the 7th International Workshop on Database and Expert Systems Applications, pages 153, IEEE Computer Society, Washington, DC, USA, 1996.Abstract & details DOI: 10.1109/DEXA.1996.558289 BibTeX
    Abstract
    In the past years, a number of implementations of temporal DBMSs has been reported. Most of these implementations share a common feature, which is that they have been built as an extension to a snapshot DBMS. In this paper, we present three alternative design approaches that can be used for extending a snapshot DBMS to support temporal data,and evaluate the suitability of each approach, with respect to a number of design objectives.
    Keywords
    -
  2. [j2]
    Spiliopoulou, M.; Hatzopoulos, M. and Vassilakis, C. A cost model for the estimation of query execution time in a parallel environment supporting pipeline. In Computers and Artificial Intelligence, 15 (4): 341-368, 1996.Abstract & details Full text BibTeX
    Abstract
    We propose a model for the estimation of query execution time in an environment supporting bushy and pipelined parallelism. We consider a parallel architecture of processors having private main memories, accessing a shared secondary storage and communicating to each other via a network. For this environment, we compute the cost of query operators when processed in isolation and when in pipeline mode. We use those formulae to incrementally compute the cost of a query execution plan from its components. Our cost model can be incorporated to any optimizer for parallel query processing that considers parallel and pipelined execution of the query operators.
    Keywords
    query cost estimation; query execution plan; query tree; pipeline; bushy parallelism; query optimisation; databases

1995

  1. [c6]
    Vassilakis, C.; Lorentzos, N. A. and Georgiadis, P. Transaction Support in a Temporal DBMS. In Proceedings of the International Workshop on Temporal Databases, pages 255-271, Springer-Verlag, London, UK, 1995.Abstract & details Full text DOI: 10.1007/978-1-4471-3033-8_14 BibTeX
    Abstract
    Transactions are a significant concept in database systems, facilitating functions both at user and system level. However transaction support in temporal DBMSs has not yet received enough research attention. In this paper, we present techniques for incorporating transaction support in a temporal DBMS, which is implemented as an additional layer to a commercial RDBMS. These techniques overcome certain limitations imposed by the underlying RDBMS, and avoid excessive increment of the log size.
    Keywords
    -

1993

  1. [j1]
    Spiliopoulou, M.; Hatzopoulos, M. and Vassilakis, C. Parallel Optimisation of Join Queries Using a Technique of Exhaustive Nature. In Computers and Artificial Intelligence, 12 (2): 145-166, 1993.Abstract & details Full text BibTeX
    Abstract
    In this study we present a technique for the parallel optimisation of join queries that uses the offered coarse-grain parallelism of the underlying architecture in order to reduce the CPU-bound optimisation overhead. The optimisation technique performs an almost exhaustive search of the solution space for small join queries and gradually, as the number of joins increases, it diverges towards iterative improvement. This technique has been developed on a low-parallelism transputer-based architecture, where its behaviour is studied for the optimisation of queries with many tens of joins.
    Keywords
    parallel optimisation, join queries, coarse-grain parallelism, transputers
  2. [c5]
    Boucouvalas, C.; Vassilakis, C. and Georgiadis, P. An Enhanced System for File Access in a Distributed UNIX Environment (Greek title: Εμπλουτισμένο σύστημα προσπέλασης αρχείων σε περιβάλλον UNIX). In Proceedings of the 4th Hellenic Conference on Informatics, 1993.(Original paper in Greek)Abstract & details BibTeX
    Abstract
    In this study we present an Enhanced File System for a Distributed Unix Environment. The Enhanced Unix File System implements a flexible protection mechanism for files and directories. It is based on the concept of Access Control Lists (ACL), which allows different permissions for files and directories to be given to specific users. His work was developed under the SunOS/NFS distributed environment, using Remote Procedure Calls (RPC) to implement the communication between the client and the server. The system consists of a daemon process working as a server and a set of client processes that provide different file and directory services. There may be running many different servers and clients over the same network. The client processes transparently locate the appropriate server for each transaction. The system also provides an open programming environment for the development of new applications. Both the user and the programmer interface of the system are kept close to standard UNIX.
    Keywords
    -
  3. [c4]
    Kassapidis, P.; Vassilakis, C.; Nikolaidou, M.; Georgiadis, P.; Votsis, Gr. and Pronios, N. Comparative Study of Protocols of the Transport Layer for Multimedia Applications (Greek title: Συγκριτική μελέτη πρωτοκόλλων επιπέδου μεταφοράς για εφαρμογές πολυμέσων). In Proceedings of the 4th Hellenic Conference on Informatics, pages 105-118, 1993.(Original paper in Greek)Abstract & details BibTeX
    Abstract
    The forthcoming use of multimedia applications will require powerful computers and high performance networks. While great progress has been made to the physical layer of networks, the upper software layers of the OSI reference model have not kept up pace with them. This paper presents the demands imposed by multimedia applications on the underlying networks and their mapping to transport layer services, that protocols implementing it must provide. Four well-known transport layer protocols are briefly presented (TCP, TP4, VMTP, HSTP/XTP). The mechanisms employed by each one of those are studied and their suitability for demanding multimedia environments are evaluated. We conclude that much more effort needs to be made on the transport layer protocols so that high performance network architectures will be available to fullfill the diverse requirements of tomorrow's multimedia applications.
    Keywords
    -
  4. [c3]
    Vassilakis, C.; Georgiadis, P.; Lelis, D.; Mouzakis, D. and Nikolaidou, M. A Methodology for the Implementation of Software for the Design of Distributed Systems (Greek title: Μεθοδολογία ανάπτυξης λογισμικού για τον σχεδιασμό κατανεμημένων συστημάτων). In Proceedings of the 4th Hellenic Conference on Informatics, pages 673-686, 1993.(Original paper in Greek)Abstract & details BibTeX
    Abstract
    As the use of distributed systems is spreading, and applications designed for such systems become more and more demanding, optimal design of distributed systems becomes a critical issue. Designing a distributed system has become more complex, due to the number of alternatives for each decision that must be made and because of the existence of many parameters which influence the overal performance of the distributed system. Thus, it is necessary to use software tools, capable of accepting a description of the user's requirements and suggesting solutions to the problem of designing a distributed system which meets the user's requirements. In this paper, we present a disciplined approach to the construction of such a software tool, which combines methods from the Artificial Intelligence domain, that are used in order to design the distributed system, along with simulation techniques, used to estimate the system's overall performance.
    Keywords
    -

1992

  1. [c2]
    Spiliopoulou, M.; Hatzopoulos, M. and Vassilakis, C. Using Parallelism and Pipeline for the Optimisation of Join Queries. In PARLE '92: Proceedings of the 4th International PARLE Conference on Parallel Architectures and Languages Europe, pages 279-294, Springer-Verlag, London, UK, 1992.Abstract & details DOI: 10.1007/3-540-55599-4_94 BibTeX
    Abstract
    In this study we present a technique for the parallel optimisation of join queries, that uses the offered coarse-grain parallelism of the underlying architecture in order to reduce the CPU-bound optimisation overhead. The optimisation technique performs an almost exhaustive search of the solution space for small join queries and gradually, as the number of joins increases, it diverges towards iterative improvement. This technique has been developed on a low-parallelism transputer-based architecture, where its behaviour is studied for the optimisation of queries with many tenths of joins.
    Keywords
    -

1990

  1. [c1]
    Hatzopoulos, M.; Gouscos, D.; Spiliopoulou, M.; Vassilakis, C. and Vazirgiannis, M. An Object-Oriented Data Model for Hypermedia Systems. In Proceedings of the DELTA Conference in Research and Development, pages 483-493, 1990. citeseer Abstract & details Full text BibTeX
    Abstract
    Hypermedia [1] is a fast growing field of research interest because of the new aspects introduced as far as it concerns the interaction between the machine and the user. The innovative features mainly refer to - the presence of various information types (multimedia environment) - the mapping of the semantic connections between information items into a flexible, efficient representation. This feature enables navigation through the information network in a meaningful way. Our effort concentrated on the definition and partial implementation of a flexible, general-purpose model through which the full capabilities of object-oriented programming can be exploited.
    Keywords
    databases