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Costas Vassilakis - Publications In Journals, Conferences and Workshops

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  1. An Object-Oriented Data Model for Hypermedia Systems, M. Hatzopoulos, D. Gouscos, M. Spiliopoulou, C. Vassilakis and M. Vazirgiannis, in Proceedings of the DELTA Conference in Research and Development, pp. 483-493, The Hague, October 1990.
    Abstract:
    • Our main objective is the definition of a design model for a hypermedia database, dedicated to accomodating multimedia information and to promote navigation as a means of information processing. We prefered the object-oriented paradigm to the relational one, because it provides generic modelling constructs and supports property inheritance. We observe the hyperbase as a network of items and links, where items contain multimedia information and links represent the relationship among them. So, we define a class hierarchy containing both the information pieces and the interconnections among them as objects in the same level of functionality. In this environment, we support typed and weighted links to enhance the declaration of semantic relationships, and keywords to allow for querying as an alternative tool for information processing.
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  2. Using Parallelism and Pipeline for the Optimisation of Join Queries, M. Spiliopoulou, M. Hatzopoulos and C. Vassilakis, in Proceedings of the PARLE Conference, Paris, June 1992.
    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.
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  3. Parallel Optimisation of Join Queries Using a Technique of Exhaustive Nature, M. Spiliopoulou, M. Hatzopoulos and C. Vassilakis, in Computers and Artificial Intelligence, Vol. 12, 1993, No. 2.
    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.
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  4. A Methodology for the Implementation of Software for the Design of Distributed Systems, C. Vassilakis, P. Georgiadis, D. Lelis, D. Mouzakis and M. Nikolaidou, Hellenic Informatics Conference, Patra 1993 (in Greek).
    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.
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  5. Comparative Study of Protocols of the Transport Layer for Multimedia Applications, P. Kassapidis, C. Vassilakis, M. Nikolaidou, P. Georgiadis, Gr. Votsis and N. Pronios, Hellenic Informatics Conference, Patra 1993 (in Greek).
    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.
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  6. An Enhanced System for File Access in a Distributed UNIX Environment, C. Boukouvalas, P. Georgiadis and C. Vassilakis, Hellenic Informatics Conference, Patra 1993 (in Greek).
    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.
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  7. Transaction Support in a Temporal DBMS, C. Vassilakis, N. Lorentzos and P. Georgiadis, in Proceedings of International Workshop on Temporal Databases, Zurich, September 1995.
    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.
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  8. A Cost Model for the Estimation of Query Execution Time in a Parallel Environment Supporting Pipeline, M. Spiliopoulou, M. Hatzopoulos and C. Vassilakis, in Journal Computers and Artificial Intelligence, Vol. 14, 1996, No. 1, pp. 341-368.
    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.
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  9. A Comparative Study of Temporal DBMS Architectures, C. Vassilakis, P. Georgiadis, A. Sotiropoulou, in Proceedings of DEXA 96 workshop, Zurich, September 1996.
    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.
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  10. Implementation of Transaction and Concurrency Control Support in a Temporal DBMS, C. Vassilakis, N. Lorentzos and P. Georgiadis, Information Systems, vol. 23, No 5, pp. 335-350, 1998.
    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 which 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.
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  11. Temporal Extension to ODMG, A. Sotiropoulou, M. Souillard, C. Vassilakis, in Proceedings of the 3rd Biennial World Conference on Integrated Design and Process Technology, Vol. 2, Issues and Applications of Database Technology (IADT), Berlin, Germany, 1998, pp. 304-311.
    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.
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  12. TOOBIS: Application of the Management of Temporal Data in Clinical Research (in French), M. Souillard, C. Vassilakis, A. Sotiropoulou, INFORSID '98 Actes des Conferences, pp. 145-168.
    Abstract:
    • Temporal data, i.e. data varying over time dimension whose history of evolutions is maintained, are not used in the industrial world. But, far from managing only non-temporal data, numerous and various applications and industrial sectors such as banking, insurance, disease management in medicine, booking and so on, face the management of temporal data. These applications often use results of own developments, simulating temporal data in a more or less effective ways.
      This paper presents the results of the European project TOOBIS - Temporal Object Oriented dataBase within Information System - underlying an application using and managing temporal data, in the domain of Clinical Research. TOOBIS offers an extension of the object-oriented database standard in order to provide a full temporal object-oriented database management system, as well as a temporal methodology of analysis and design.
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  13. Implementing Embedded Valid Time Query Languages, C. Vassilakis, P. Georgiadis, T. Selis, Proceedings of the DEXA '98 Conference, pp. 561-572.
    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.
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  14. Is Server-Side Programming Killing Your Web Server?, C. Vassilakis, G. Lepouras, Poster presentation in ActiveWeb 99.
    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.
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  15. Distributed information systems tailorability: A component approach, Dimitrios Theotokis, George-Dimitrios Kapos, Costas Vassilakis, Anya Sotiropoulou and Georgios Gyftodimos, Proceedings of the IEEE Workshop on Future Trends on Distributed Computing, Cape Town, 1999, pp. 95-101.
    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 run-time, 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.
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  16. An Optimization Scheme for Coalesce/Valid Time Selection Operator, Costas Vassilakis, SIGMOD Record, vol. 29, number 1, March 2000, pp. 38-43.
    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.
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  17. Multilingual Web Site Construction and Maintenance, George Lepouras and Costas Vassilakis, Proceedings of the SCI 2000 conference, Vol. I, Orlando, Florida, USA, pp. 56-61.
    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.
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  18. An approach to designing and implementing virtual museums, D. Charitos, G. Lepouras, C. Vassilakis, V. Katifori and L. Halatsi, Proceedings of the seventh UK VR-SIG Conference, Glasgow, 2000.
    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.
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  19. Function Oriented History Representation in Databases, L. Kovacs and C. Vassilakis, Computers and Artificial Intelligence, vol. 19, 2000, pp. 417-444.
    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 at the end of the paper by a hospital example.
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  20. Building a VR - Museum in a Museum, G. Lepouras, D. Charitos, C. Vassilakis, A Charissi and L. Halatsi, To appear in Third International Virtual Reality Confere nce, VRIC2001, Laval, France, May 16-20, 2001.
    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.
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  21. Designing a virtual museum within a museum, D. Charitos, G. Lepouras, C. Vassilakis, V. Katifori, A. Charissi, L. Halatsi, Proceedings of the VAST2001 Symposium, November 2001, Athens, Greece.
    Abstract:
    • A virtual environment system installed within a real museum can offer a number of advantages, which are discussed in this paper: overcoming the lack of exhibition space, responding to the need for interaction with certain exhibits, affording easy transfer of exhibitions to remote sites. This paper also presents an approach towards designing and developing a virtual reality museum comprising ten different museums. The processes of digitisation, architectural design and exhibit presentation are outlined and points of particular importance are explained. Exhibits from real world museums have been digitised and integrated in this VE.
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  22. e-Citizens and e-Consumers: Is There a Difference?, G. Laskaridis, C. Vassilakis, G. Lepouras, S. Rouvas, Proceedings of the PCHCI 2001 Workshop: "Transforming Web Surfers to E-Shoppers", Patras, Greece, December 2001, pp. 47-50.
    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.
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  23. Serving Enhanced Hypermedia Information, G. Lepouras, C. Vassilakis, G. R. S. Weir, Proceedings of the ECIR02, 24th BCS-IRSG European Colloquium on IR Research, 24th BCS-IRSG European Colloquium on IR Research, Lecture Notes in Computer Science 2291, pp. 86-92, Springer-Verlag Berlin Heidelberg 2002, pp. 86-92.
    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.
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  24. SMARTGOV: A Governmental Knowledge-based Platform for Public Sector Online Services, E. Tambouris, G. Boukis, C. Vassilakis, G. Lepouras, S. Rouvas, R. Canadas, S. Heredia, J. C. Lopez Usero, Proceedings of the KMGov2002 Workshop, Copenhagen, Denmark, May 23-24, 2002, pp. 173-185.
    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.
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  25. A system to support dissemination of knowledge and sharing of experiences in the working environment, G.Lepouras, C.Vassilakis and G. R. S. Weir, International Journal of Continuing Engineering Education and Life-Long Learning, Special Edition: Technological Support for New Educational Perspectives, vol. 13 no. 3/4, 2003, pp. 248-257.
    Abstract:
    • In the information era enterprises strive to be productive and efficient. One feature of this goal is to engage their employees in education programmes, help them gain new experiences and knowledge and adapt to an ever-changing working environment. Such programmes require thorough design in order to achieve satisfactory results. Lately, enterprises recognising the role 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, 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.
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  26. Controlled Caching of Dynamic WWW Pages, C. Vassilakis and G. Lepouras, Proceedings of the DEXA 2002 conference, pp. 9-18
    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.
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  27. Transactional e-Government Services: an Integrated Approach, C. Vassilakis, G. Laskaridis, G. Lepouras, S. Rouvas and P. Georgiadis, Proceedings of the 1st International Conference on Electronic Government-EGOV 2002, pp. 276-279
    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.
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  28. A Governmental Knowledge-based Platform for Public Sector Online Services, P. Georgiadis, G. Lepouras, C. Vassilakis, G. Boukis, T. Tambouris, S. Gorilas, E. Davenport, A. Macintosh, J. Fraser and D. Lochhead, Proceedings of the 1st International Conference on Electronic Government-EGOV 2002, pp. 362-369.
    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.
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  29. An Object-Oriented Approach for Designing Administrative e-Forms and Transactional e-Services, D. Gouscos, S. Rouvas, C. Vassilakis and P. Georgiadis, Proceedings of the OOIS 2002 conference, pp. 19-30.
    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.
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  30. A Framework for Managing the Lifecycle of Transactional e-Government Services, C. Vassilakis, G. Laskaridis, G. Lepouras, S. Rouvas, P. Georgiadis, Telematics and Informatics, vol. 20/4, pp 315-329, 2003, Elsevier Science Publications Ltd..
    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.
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  31. Facilitating VR Museums Web Presence, George Lepouras, Akrivi Katifori, Costas Vassilakis, Anna Charissi, Proceedings of HCI 2003, vol. 4, pp. 1143-1147.
    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.
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  32. Improving e-form layout through analysis of form semantics and validation checks, Costas Vassilakis, George Lepouras, Stathis Rouvas, Panagiotis Georgiadis, Proceedings of the CAiSE 2003 Forum, pp. 149-152.
    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.
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  33. Integrating e-Government Public Transactional Services in the Public Authority Workflow, Costas Vassilakis, George Lepouras, Stathis Rouvas, Panagiotis Georgiadis, Electronic Government, vol. 1, No 1, pp. 49-60.
    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.
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  34. E-forms services for the Public Sector: Shifting Development Effort from Programmers to Domain Experts, Stelios Gorilas, Kostas Vassilakis, Tomas Pariente Lobo, Efthimios Tabouris, to appear in the proceedings of e-Challenges 2003.
    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.
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  35. Tailorability in the context of E-government Information Systems: An approach, George Lepouras, Anya Sotiropoulou, Dimitrios Theotokis, Costas Vassilakis, to appear in the proceedings of the IRMA 2004 conference.
    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.
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  36. Content enrichment through dynamic annotation, George Weir, George Lepouras, Costas Vassilakis to appear in the proceedings of the 6th International Conference on Enterprise Information Systems
    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 means of modifying the content displayed to local users by addition, removal or reforming 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. Once again, this is illustrated in two contexts (intra-group support and inter-group support). These differing applications have a common goal which is to enrich the knowledge content of the materials placed before the user. Dynamic annotation provides a potent and flexible means to this end.
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  37. Real exhibitions in a virtual museum, George Lepouras, Akrivi Katifori, Costas Vassilakis, Dimitrios Charitos to appear in Virtual Reality, Springer-Verlag
    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.
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  38. Adaptive Virtual Museums on the Web, George Lepou ras and Costas Vassilakis, to appear as a book chapter in the book "Adaptable and Adaptive Hypermedia Systems" Sherry Y. Chen and George Magoulas (eds)..
    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.
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  39. A Web Browser for ISDN Card Phones, Dimitris Maro ulis, Sotiris Aronis, Vassiliki Nassiopoulou, Nikos Grammenos, Costas Vassilakis, to appear in the Journal of Internet Technology.
    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.
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  40. Virtual Museums for all: Employing Game Technology for Edutainment, George Lepouras, Costas Vassilakis, to appear in the Virtual Reality Journal.
    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.
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  41. Exploiting Form Semantics and Validation Checks to Improve e-Form Layout, Costas Vassilakis, George Lepouras, Stathis Rouvas and Panagiotis Georgiadis, to appear in the International Journal of Web Engineering and Technology.
    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.
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  42. An XML model for electronic services, Costas Vassilakis, George Lepouras, Constantin Halatsis and Tomas Pariente Lobo, to appear in Electronic Government.
    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.
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  43. Reusability in Electronic Services Development, Costas Vassilakis, George Lepouras, to appear in the proceedings of the CSITeA 04 conference.
    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.
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  44. A Flexible Framework for Managing Temporal Clinical Trial Data, Michael Souillard , Carine Souveyet, Costas Vassilakis, Anya Sotiropoulou, to appear in the International Journal of Electronic Healthcare.
    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.
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  45. Barriers To Electronic Service Development, Costas Vassilakis, George Lepouras, John Fraser, Simon Haston, Panagiotis Georgiadis, to appear in the e-Service Journal.
    Abstract:
    • E-government initiatives have been proven to deliver significant benefits, both for suppliers of electronic services (public authorities and organisations) 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 given in this paper.
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  46. A Blackboard-oriented Architecture for e-Government service composition, Costas Vassilakis, Anya Sotiropoulou, Dimitrios Theotokis, Dimitris Gouscos, to appear in the proceedings of the IRMA 2005 conference.
    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.
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  47. An Active Ontology-based Blackboard Architecture for Web Service Interoperability, George Lepouras, Costas Vassilakis, Anya Sotiropoulou, Dimitrios Theotokis, Akrivi Katifori, to appear in the proceedings o f the Second IEEE Conference on Service Systems and Service Management.
    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.
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  48. Ontology for e-Government public services, Costas Vassilakis, George Lepouras, to appear in the Encyclopedia of E-Commerce, E-Government and Mobile Commerce.
    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.
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  49. Tailorable e-government information systems, George Lepouras, Anya Sotiropoulou, Dimitrios Theotokis, Costas Vassilakis, to appear in the Encyclopedia of E-Commerce, E-Government and Mobile Commerce.
    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.
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  50. Adaptive Virtual Reality Shopping Malls, George Lepouras, Costas Vassilakis, to appear in the Encyclopedia of E-Commerce, E-Government and Mobile Commerce.
    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.
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  51. A Semantics-Based Consultations Workbench, Costas Vassilakis, Dimitris Gouscos, Panagiotis Georgiadis, to appear in the proceedings of the 2005 ITI 3rd International Conference on Information and Communication Technology (IEEE).
    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.
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  52. Domain Expert User Development: The SmartGov Approach, George Lepouras, Costas Vassilakis, Constantin Halatsis, Panagiotis Georgiadis, To appear in Communications of the ACM.
    Abstract:
    • End-user development (EUD) aims to empower end-users with the necessary tools to implement their own software. In this sense domain expert user development can be viewed as a special case of EUD. Domain experts can be considered to be a special case of end-users who possess the necessary knowledge of how the software should operate, what tasks it has to carry out, which business rules need to be enforced, validation checks to perform, etc. It has to be noted that in some cases domain experts will not use the produced software themselves, this software however will indirectly support their work, e.g. software developed by tax officers (domain experts) to be used by tax payers (actual end-users) simplifies the subsequent work of tax officers through minimization of errors, population of electronic data repositories etc.
      Using a user-centred software engineering paradigm domain expert users will work along with software developers to create specifications for the software to be implemented by the latter group. This process is usually iterative. Domain experts will be questioned by developers, developers will design a first prototype, the domain experts will most probably ask for changes, developers will come back with an altered prototype, etc. Since both user groups are usually involved in other assignments as well, this process can be time-consuming. Impedance mismatch problems, i.e. problems in the communication between the domain experts and the IT staff due to different backgrounds, perspectives and terminology result into additional delays within this phase. An alternative to this would be to help domain experts to create the software with a minimum or no involvement of IT personnel. This is the approach adopted in the SmartGov project . In the framework of SmartGov a knowledge-based platform was developed that assists public sector employees with suitable domain expertise to generate online transaction services by simplifying their development, maintenance and integration with installed IT systems.
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  53. The Lifecycle Of Transactional Services, Costas Vassilakis, George Lepouras, To appear in the Encyclopedia of Digital Government.
    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.
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  54. Reusability In Governmental Electronic Services, George Lepouras, Costas Vassilakis, To appear in the Encyclopedia of Digital Government.
    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.
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  55. Visualizing a Temporally-Enhanced Ontology, Katifori Akrivi, Vassilakis Costas, Lepouras Georgios, Daradimos Ilias, Halatsis Constantin, To appear in the proceedings of the ACM Advanced Visual Interfaces 06 Conference.
    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.
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  56. A Comparative Study of Four Ontology Visualization Techniques in Protege: Experiment Setup and Preliminary Resu lts, Akrivi Katifori , Elena Torou, Constantin Halatsis, Lepouras Georgios and Costas Vassilakis, To appear in the proceedings of the IV 06 Conference.
    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.
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  57. A Context-Based Adaptive Visualization Environment, Maria Golemati, Constantin Halatsis, Costas Vassilakis, Akrivi Katifori, Georgios Lepouras, To appear in the proceedings of the IV 06 Conference.
    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.
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  58. Web Service Execution Streamlining, Costas Vassilakis, George Lepouras, Akrivi Katifori, To appear in the proceedings of the the Third IEEE Conference on Service Systems and Service Management - ICSSSM 06.
    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.
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  59. A Knowledge-Based Approach for Developing Multi-Channel e-Government Services, Costas Vassilakis, George Lepouras, Constantin Halatsis, To appear in the journal of Electronic Commerce Research and Applications.
    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.
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  60. Reverse-engineering electronic services, Costas Vassilakis, George Lepouras, Akrivi Katifori, To appear in the Proceedings of the 1st International Conference on Software and Data Technologies (ICSOFT 2006).
    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.
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  61. Creating an Historical Archive Ontology: Guidelines and Evaluation, Torou Elena, Katifori Akrivi, Vassilakis Costas, Lepouras Georgios, Halatsis Constantin, To appear in the Proceedings of the 1st International Conference on Digital Information Management (ICDIM 2006).
    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.
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  62. Towards Dynamic, Relevance-Driven Exception Resolution in Composite Web Services, Kareliotis Christos, Vassilakis Costas, Georgiadis Panagiotis, To appear in the Proceedings of OOPSLA 2006, Fourth International Workshop on SOA & Web Services Best Practices
    Abstract:
    • Web services have become the leading technology for application-to-application (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.
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  63. Performance Analysis of Multistage Interconnection Networks determining optimal parameters for data-intensive business applications, D.C. Vasiliadis, G.E. Rizos, and C. Vassilakis, to appear in the Proceedings of the 7th IBIMA Conference, 2006
    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.
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  64. Performance analysis of blocking banyan switches, D.C. Vasiliadis, G.E. Rizos, and C. Vassilakis, to appear in the Proceedings of the IEEE sponsored International Joint Conference on Computer, Information and System Sciences and Engineering - CIS2E 06
    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.
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  65. Towards a P2P world: peered taxation, M. Kalikakis, D. Gouscos, K. Vassilakis, P. Georgiadis, to appear in the Proceedings of the 2nd International Workshop "E-taxation: State & Perspectives"
    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.
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  66. Historical Archive Ontologies - Requirements, Modeling and Visualization, Katifori Akrivi, Torou Elena, Vassilakis Costas, Lepouras Georgios, Halatsis Constantin, Daradimos Elias, to appear in the proceedings of the First IEEE International Conference on Research Challenges in Information Science (RCIS), Morocco 2007
    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.
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  67. Creating an Ontology for the User Profile: Method and Applications, Maria Golemati, Akrivi Katifori, Costas Vassilakis, George Lepouras, Constantin Halatsis, to appear in the proceedings of the First IEEE International Conference on Research Challenges in Information Science (RCIS), Morocco 2007
    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.
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  68. Component Reuse in Electronic Services Development, Costas Vassilakis, George Lepouras to appear in a special issue of the Journal of Computational Methods in Science and Engineering
    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.
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  69. Ontology Visualization Methods - A Survey, Akrivi Katifori, Constantin Halatsis, George Lepouras, Costas Vassilakis, Eugenia Giannopoulou to appear in ACM Computing Surveys
    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 also be adapted for ontology representation. The purpose of this work 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.
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  70. Performance Analysis of dual priority single-buffered blocking Multistage Interconnection Networks, D. C. Vasiliadis , G. E. Rizos , C. Vassilakis to appear in the Proceedings of ICNS 07, IEEE press
    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.
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  71. Evaluating the Significance of the Windows Explorer Visualization in Personal Information Management Browsing tasks, Maria Golemati, Akrivi Katifori, Eugenia G. Giannopoulou, Ilias Daradimos, Costas Vassilakis, to appear in the Proceedings of Information Visualization 07, IEEE press
    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 interviews and an experiment.
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  72. Enhancing BPEL scenarios with Dynamic Relevance-Based Exception Handling, Chris Kareliotis, Costas Vassilakis, Panayiotis Georgiadis, Proceedings o f the IEEE 2007 International Conference on Web Services (ICWS)
    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.
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  73. An Approach for re-engineering the Taxation Process to Support Participatory Decisions on Tax Budget Allocation Manolis Kalikakis, Dimitris Gouscos, Costas Vasillakis, Panagiotis Georgiadis, Proceedings of the 1st International Conference on Methodologies, Technologies and Tools enabling e-Government
    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.
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  74. Performance Analysis of two-priority network schema for single-buffered delta networks, D. C. Vasiliadis, G. E. Rizos, C. Vassilakis, E. Glavas, Proceedings of The 18th Annual IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC'07), CAMAD 07 Workshop
    Abstract:
    • In this paper a novel two-priority network schema is presented, and exemplified through its application on single-buffered 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.
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  75. Exploiting Context in Mobile Applications, Benou Poulcheria, Vassilakis Costas, To appear in Encyclopedia of Information Science and Technology, Second Edition
    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.
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  76. Virtual reality in the e-Society, G. D. Magoulas, G. Lepouras, C. Vassilakis, Virtual Reality Journal, Special issue "Virtual reality in the e-Society", editorial preface
    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.
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  77. Mobile and Context-Aware e-Commerce: Issues, Challenges and Research Directions, Costas Vassilakis, George Lepouras, Spiros Skiadopoulos, Journal of Electronic Commerce in Organizations, Special Issue Editorial Preface
    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.
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  78. The role of priority mechanisms on performance metrics of double-buffered Switching Elements, D. C. Vasiliadis, G. E. Rizos, C. Vassilakis, Proceedings of ICCMSE 2007
    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.
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  79. Performance Evaluation of Distance Vector Routing Protocol on a Wireless Circular Model, D. C. Vasiliadis, G. E. Rizos, C. Vassilakis, Proceedings of the IEEE sponsored International Joint Conference CISSE 2007
    Abstract:
    • In this paper, a wireless Circular Model over the Distance Vector routing protocol is presented and analyzed. The performance of this algorithm, 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.
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  80. An Active Blackboard for Service Discovery, Composition and Execution, George Lepouras, Costas Vassilakis, Anya Sotiropoulou, Dimitrios Theotokis, Akrivi Katifori, to appear in the International Journal of e-Government
    Abstract:
    • Organisations nowadays are in the process of developing network-enabled systems through which they deliver electronic services to citizens, customers and enterprises. Often, such services need to be combined in order to cover all aspects of a service consumer’s life event. The composition of different services though is usually left to the service consumer, who needs to manually locate the individual services and drive the process of obtaining results from some services and feeding them as input to subsequent ones until all relevant services have been executed. Although it would be possible for organisations to improve their level of service through provision of composite services, realizing thus the concept of one-stop government, i.e. by making available mechanisms that would undertake the task of input collection, invocation and execution synchronisation of individual services and delivery of the final result as a reply, such facilities have not been made yet widely available. This shortage stems partly from financial considerations, since the frequent changes in the regulatory framework of both the individual services and in their interoperation requirements or in the technical aspects of the service implementation render the development and maintenance of composite services inexpedient and partly from technical issues, since format or representational incompatibilities in parameters and results hinders automation developments. In this paper we present an active blackboard architecture, which automates the task of service composition based on the semantics of individual services and the data dependencies between them. The blackboard incorporates registries, which can be employed for facilitating service discovery and an execution engine that arranges for dynamic service composition and execution.
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  81. Personal Ontology Creation and Visualization for a Personal Interaction Management System, Akrivi Katifori, Costas Vassilakis, Ilias Daradimos, George Lepouras, Yannis Ioannidis, Alan Dix, Antonella Poggi, Tiziana Catarci, Proceedings of PIM, CHI 2008,
    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.
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  82. Using Spreading Activation through Ontologies to Support Personal Information Management, Akrivi Katifori, Costas Vassilakis, Alan Dix, Proceedings of CSKGOI, within IUI 2008,
    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.
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  83. Context and Adaptivity-Driven Visualization Method Selection, Maria Golemati, Costas Vassilakis, Akrivi Katifori, George Lepouras, Constantin Halatsis, Chapter in "Intelligent User Interfaces: Adaptation and Personalization Systems and Technologies",
    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.
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  84. Improving Performance of Finite-buffered Blocking Delta Networks with 2-class Priority Routing through Asymmetric-sized Buffer Queues, D. C. Vasiliadis, G. E. Rizos, C. Vassilakis, Proceedings of the Fourth Advanced International Conference on Telecommunications AICT 2008, IEEE Press,
    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 compared 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.
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  85. Selected Results of a Comparative Study of Four Ontology Visualization Methods for Information Retrieval tasks, Akrivi Katifori, Elena Torou, Costas Vassilakis, Georgios Lepouras, Constantin Halatsis, Proceedings of IEEE RCIS 2008,
    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 Protege.
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  86. WhereRU: GPS position reporting and a personal ontology as a virtual community utility, I. Daradimos, A. Katifori, C. Vassilakis, Proceedings of IEEE RCIS 2008,
    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.
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  87. A Heuristics-Based Approach to Reverse Engineering of Electronic Services, Costas Vassilakis, George Lepouras, Akrivi Katifori, to appear in Information and Software Technology,
    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.
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  88. An Interview-Based User Study on the use of Visualizations for Folder Browsing, Maria Golemati, Akrivi Katifori, Eugenia G. Giannopoulou, Ilias Daradimos, Costas Vassilakis, George Lepouras, Constantin Halatsis, Proceedings of IV 08,
    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, namely 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 interview-based user study.
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  89. Supporting Research in Historical Archives: Historical Information Visualization and Modeling Requirements, Akrivi Katifori, Elena Torou, Costas Vassilakis, Constantin Halatsis, Proceedings of IV 08,
    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.
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  90. An Integrated Environment for Cataloguing and Online Presentation of Museum Exhibits, Costas Vassilakis, Akrivi Katifori, Elias Daradimos and George Lepouras, DESIDOC Journal of Library and Information Technology, Vol. 28, No. 4, July 2008, pp. 72-78,
    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.
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  91. Routing and Performance Analysis of Double-Buffered Omega Networks Supporting Multi-Class Priority Traffic, D. C. Vasiliadis, G. E. Rizos, C. Vassilakis, E. Glavas, Proceedings of ICSNC 2008, IEEE press
    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.
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  92. A Game-Engine Based Virtual Museum Authoring and Presentation System, Victor Mateevitsi, Michael Sfakianos, George Lepouras, Costas Vassilakis, Proceedings of ACM DIMEA 2008
    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.
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  93. Exception Resolution for BPEL Processes: a Middlewarebased Framework and Performance Evaluation, Christos Kareliotis, Costas Vassilakis, Efstathios Rouvas and Panayiotis Georgiadis Proceedings of the tenth International Conference on Information Integration and Web-based Applications & Services (iiWAS2008)
    Abstract:
    • WS-BPEL has become the predominant technology for specifying and executing composite business processes within the Service Oriented Architecture. During the execution however of such a composite business process, a number of faults stemming from the distributed nature of the SOA architecture (e.g. network or server failures) may occur. To this end, the WS-BPEL scenario designer must exploit the provisions offered by WS-BPEL to catch exceptions owing to system failures and resolve them, typically by invoking some alternate equivalent web service that is expected to be reachable and available. The task of system fault handler specification is though an additional burden for the WS-BPEL scenario designer and the presence of such handlers within the WS-BPEL scenario necessitates additional maintenance activities, as new alternate services become available 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 faults within the scenarios. We also present performance measures, establishing that the overhead imposed by the addition of the proposed middleware layer is minimal.
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  94. Ontologies as Tools for Historians, Akrivi Katifori, Costas Vassilakis, poster presentation in the International Symposium on Information & communication technologies in cultural heritage, Ioannina, Greece, October 16-18, 2008
    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.
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  95. A Drupal CMS Module for Managing Museum Collections, Daradimos Ilias, Costas Vassilakis Akrivi Katifori, poster presentation in the International Symposium on Information & communication technologies in cultural heritage, Ioannina, Greece, October 16-18, 2008
    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.
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  96. Evaluation study of a wireless multimedia traffic-oriented network model, D. C. Vasiliadis, G. E. Rizos, C. Vassilakis, AIP conference proceedings 1060 (procs. of IECCS 2007), pp. 379-384, 2008
    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.
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  97. Performance Evaluation of Multicast Routing over Multilayer Multistage Interconnection Networks, D. C. Vasiliadis, G. E. Rizos, C. Vassilakis, E. Glavas Proceedings of the Fifth Advanced International Conference on Telecommunications (AICT 2009), IEEE press
    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.
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  98. Ontologies and the Brain: Using Spreading Activation through Ontologies to Support Personal Interaction, Akrivi Katifori, Costas Vassilakis, Alan Dix Cognitive Systems Research, Special Issue on Brain Informatics
    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.
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  99. Routing and Performance Evaluation of Dual Priority Delta Networks under Hotspot Environment, D. C. Vasiliadis, G. E. Rizos, C. Vassilakis, Proceedings of Conference on Advances in Future Internet (AFIN 2009), IEEE Press
    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.
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  100. QoS-Driven Adaptation of BPEL Scenario Execution,, Kareliotis Christos, Costas Vassilakis, Efstathios Rouvas, Panayiotis Georgiadis, Proceedings of IEEE International Conference on Web Services, 2009
    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.
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  101. QoS-aware Exception Resolution for BPEL Processes: A Middleware-based Framework and Performance Evaluation,, Kareliotis Christos, Costas Vassilakis, Efstathios Rouvas, Panayiotis Georgiadis, to appear in the International Journal on Web and Grid Services (IJWGS)
    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 process of selecting the alternate services to be invoked can be driven by process consumerspecified QoS policy, specifying lower and upper bounds for each QoS attribute as well as the importance of each QoS parameter. 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 WSBPEL 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.
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  102. A framework for adaptation in secure web services, Costas Vassilakis, Kareliotis Christos, Proceedings of MCIS 2009
    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.
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  103. Visualizing Hierarchies: Evaluating the Efficiency and Cognitive Effects of S ix Visualization Techniques for Browsing and Management Tasks, Golemati, Marianthi, Vassilakis, Costas, Katifori, Akrivi, Lepouras, George, Halatsis, Constantin, Poster presentation in IV 09
    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.
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  104. Capturing the historical research methodology: an experimental approach, Torou Elena, Katifori Akrivi, Vassilakis Costas, Lepouras Georgios, Halatsis Constantin, Proceedings of International Conference of Education, Research and Innovation (ICERI 2009), Madrid, November 16-18, 2009
    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.
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  105. Spreading Activation Over Ontologies: From Personal Context To Web Scale Reasoning, Alan Dix, Akrivi Katifori, Giorgos Lepouras, Costas Vassilakis and Nadeem Shabir To appear in the International Journal of Semantic Computing, Special issue on Web Scale Reasoning
    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.
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  106. A methodology for the design of online exhibitions, Angeliki Antoniou, George Lepouras and Costas Vassilakis To appear in DESIDOC Journal of Library and Information Technology, Special Issue on Online Exhibitions
    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.
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  107. The Conceptual Model of Context for Mobile Commerce Applications, Benou Poulcheria, Vassilakis Costas, To appear in Electronic Commerce Research, Springer-Verlag
    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.
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  108. From the Web of Data to a World of Action, Alan Dix, Giorgos Lepouras, Akrivi Katifori, Costas Vassilakis, Tiziana Catarci, Antonella Poggi, Yannis Ioannidis, Miguel Mora, Ilias Daradimos, Nazihah Md.Akim, Shah Rukh Humayoun, Fabio Terella.
    To appear in Journal of Web Semantics
    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.
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  109. Improving performance of a wireless multimedia traffic-oriented network through prediction of routing, D. C. Vasiliadis, G. E. Rizos, C. Vassilakis, International Journal on Information Technologies & Security, no 3, 2010
    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.
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  110. Historical research in archives: user methodology and supporting tools, Elena Torou, Akrivi Katifori, Costas Vassilakis, George Lepouras, Constantin Halatsis, to appear in International Journal of Digital Libraries, Springer-Verlag
    Abstract:
    • Historic research involves finding, using and correlating information within 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 paper, we 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 documents within historical source repositories and building tools that will enable historians to access the needed information more rapidly and fully.
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  111. Modelling and performance evaluation of a novel internal priority routing scheme for finite-buffered multistage interconnection networks, D. C. Vasiliadis, G. E. Rizos, C. Vassilakis and E. Glavas, to appear in International Journal of Parallel, Emergent and Distributed Systems, Taylor & Francis
    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.
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  112. Performance Analysis of Dual-Priority Multilayer Multistage Interconnection Networks under Multicast Environment, D. C. Vasiliadis, G. E. Rizos, C. Vassilakis, to appear in Journal of Networks, Academy publishers
    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 factor, 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.
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  113. Performance Study of Multi-Layered Multistage Interconnection Networks under Hotspot Traffic Conditions, D. C. Vasiliadis, G. E. Rizos, C. Vassilakis to appear in Journal of Computer Systems, Networks, and Communications, Hindawi Publishing Corporation
    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.
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  114. Spreading Activation for Web Scale Reasoning: Promise and Problems, Nazihah Md. Akim, Alan Dix, Akrivi Katifori, Giorgos Lepouras, Nadeem Shabir, Costas Vassilakis ACM WebSci 11, poster presentation
    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.
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  115. A Software Architecture for Provision of Context-Aware Web-based m-Commerce Applications, Poulcheria Benou and Costas Vassilakis Proceedings of the 11th IEEE International Conference on Computer and Information Technology (CIT 2011)
    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.
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  116. Wikis in enterprise settings: a survey, Lykourentzou Ioanna, Dagka Foteini, Papadaki Katerina, Lepouras Giorgos and Vassilakis Costas, Enterprise Information Systems. First published on: 14 June 2011 (iFirst) DOI: 10.1080/17517575.2011.580008, URL: http://dx.doi.org/10.1080/17517575.2011.580008.
    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.
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  117. A methodological framework for the cognitive-behavioural evaluation of educational e-games, Angeliki Antoniou, Dimitris Diakakis, George Lepouras and Costas Vassilakis, To appear in International Journal of Learning Technology.
    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.
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  118. Performance Analysis of Multi-Layered Multi-Priority Assymetric-Sized Delta Networks, D. C. Vasiliadis, G. E. Rizos, C. Vassilakis to appear in Journal of Computer Networks, and Communications, Hindawi Publishing Corporation.
    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.
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  119. Supporting User Roles in Ontology Fuzzification, Manolis Wallace, Panos Alexopoulos, Ioannis Papafragkos and Costas Vassilakis Proceedings of the 6th International Workshop on Semantic media adaptation and personalization, December 1-2, 2011 Vigo (Spain), IEEE press.
    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.
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  120. OntoFM: A Personal Ontology-based File Manager for the Desktop, Rompa, J., Lepouras, G., Vassilakis C., and Tryfonopoulos, C. Demo at the 10th International Web Conference, 2011, Bonn, Germany.
    Abstract:
    • OntoFM is a novel file manager that bases its interactivity on the user’s personal ontology, offering semantic browsing and searching mechanisms for locating files, a mind map inspired ontology visualization, and simple-to-use intuitive functionality that encourages less experienced users. The implementation of OntoFM is based on Protege, an extensible open source ontology editor and knowledge-base framework. The file manager is implemented as a Protege tab widget, retrieving information from your personal ontology. Ontology visualization is based upon the OntoGraf plug-in which has been extended to comply with the mind map paradigm. Currently the ontology visualization pane permits only navigational functions, while other ontology management functions have been hidden to ease the complexity of the user interface.
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  121. A distributed recommender system architecture, Panagiotis Giannikopoulos and Costas Vassilakis International Journal of Web Engineering and Technology, vol 7(3), 2012.
    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.
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  122. Class-Based Weighted Fair Queuing Scheduling on Dual-Priority Delta Networks, D. C. Vasiliadis, G. E. Rizos, C. Vassilakis To appear in Journal of Computer Networks and Communications.
    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.
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  123. Context Management for m-Commerce Applications: Determinants, Methodology and the Role of Marketing, Poulcheria Benou, Costas Vassilakis, Adam Vrechopoulos To appear in Information Technology and Management vol. 13, pp. 91.111, 2012, Springer-Verlag.
    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.
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  124. A context management architecture for m-commerce applications, Poulcheria Benou, Costas Vassilakis To appear in Central European Journal of Computer Science, Versita, co-published with Springer Verlag.
    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.
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  125. Class-Based Weighted Fair Queuing Scheduling on Quad-Priority Delta Networks, D. C. Vasiliadis, G. E. Rizos, C. Vassilakis to appear in International Journal of Parallel, Emergent and Distributed Systems, Taylor & Francis.
    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.
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  126. An integrated framework for QoS-based adaptation and exception resolution in WS-BPEL scenarios, D. Margaris, C. Vassilakis and P. Georgiadis Proceedings of the 2013 ACM Symposium on Applied Computing, SOAP track.
    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.
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  127. Modelling and performance study of finite-buffered blocking Multistage Interconnection Networks supporting natively 2-class priority routing traffic, D. C. Vasiliadis, G. E. Rizos, C. Vassilakis, to appear in Journal of of Network and Computer Applications, Elsevier.
    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.
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  128. Adapting WS-BPEL scenario execution using collaborative filtering techniques, D. Margaris, P. Georgiadis, C. Vassilakis Proceedings of the IEEE RCIS 2013 conference.
    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.
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  129. Improving museum visitors' Quality of Experience through intelligent recommendations: A visiting style-based approach, Ioanna Lykourentzou, Xavier Claude, Yannick Naudet, Eric Tobias, Angeliki Antoniou, George Lepouras and Costas Vasilakis, Proceedings of MASIE 2013 Workshop, co-located with the 9th International Conference on Intelligent Environments IE'13.
    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.
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  130. User Profiling: Towards a Facebook Game that Reveals Cognitive Style, Angeliki Antoniou, Ioanna Lykourentzou, Jenny Rompa, Eric Tobias, George Lepouras, Costas Vassilakis, Yannick Naudet. Proceedings of the GALA 2013 conference, Paris, October 2013.
    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.
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  131. Mindmap-Inspired Semantic Personal Information Management, Jenny Rompa, Christos Tryfonopoulos, Costas Vassilakis, George Lepouras Demo at the 17th International Conference on Extending Database Technology, 2014, Athens, Greece.
    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.
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  132. Performance Tuning of Dual-priority Delta Networks through Queuing Scheduling Disciplines, D. C. Vasiliadis, G. E. Rizos, C. Vassilakis, Journal of Communications Software and Systems, vol. 9, no. 4, December 2013, pp. 222-235.
    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.
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  133. Towards a Learning Analytics Platform for Supporting the Educational Process, George Lepouras, Akrivi Katifori, Costas Vassilakis, Angeliki Antoniou, Nikos Platis, Proceedings of the 5th Conference on Information, Intelligence, Systems & Application (IISA2014).
    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.
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  134. Visualization method effectiveness in ontology-based information retrieval tasks involving entity evolution, Akrivi Katifori, Costas Vassilakis, George Lepouras, Elena Torou, Constantin Halatsis Proceedings of SMAP 2014.
    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.
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  135. An integrated framework for adapting WS-BPEL scenario execution using QoS and collaborative filtering techniques, D. Margaris, C. Vassilakis, P. Georgiadis Science of Computer Programming 98(2015) 707.734.
    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.
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  136. A Hybrid Framework for WS-BPEL Scenario Execution Adaptation, Using Monitoring and Feedback Data, D. Margaris, C. Vassilakis, P. Georgiadis Proceedings of ACM SAC 2015.
    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.
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  137. A Collaborative Filtering Algorithm with Clustering for Personalized Web Service Selection in Business Processes, Dionisis Margaris, Panagiotis Georgiadis, Costas Vassilakis Proceedings of RCIS 2015.
    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.
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  138. Effectiveness of visualization for information retrieval through ontologies with entity evolution: the impact of ontology modelling, Akrivi Katifori, Costas Vassilakis, George Lepouras, Elena Torou International Journal of Information Retrieval Research 5(2), 2015.
    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.
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  139. On Replacement Service Selection in WS-BPEL Scenario Adaptation, D. Margaris, P. Georgiadis, Costas Vassilakis Proceedings of the 8th IEEE International Conference on Service Oriented Computing & Applications.
    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.
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  140. A mobile-enabled platform for presenting and disseminating cultural heritage information enhanced with augmented reality (in Greek), K. Masselos, C. Vassilakis, G. Lepouras, C. Trifonopoulos, N. Tselikas, N. Platis, 1st Panhellenic Conference on Cultural Heritage Digitization.
    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.
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  141. Improving QoS Delivered by WS-BPEL Scenario Adaptation through Service Execution Parallelization, D. Margaris, C. Vassilakis, P. Georgiadis Proceedings of the ACM Symposium on Applied Computing, 2016.
    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 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.
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  142. The use of semantics in the CrossCult H2020 project, Stavroula Bampatzia, Omar Gustavo Bravo-Quezada, Angeliki Antoniou, Martin Lopez Nores, Manolis Wallace, George Lepouras and Costas Vasilakis Proceedings of the second International KEYSTONE Conference, (IKC2016), 2016
    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.
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  143. Interconnecting Objects, Visitors, Sites and (Hi)Stories across Cultural and Histori cal Concepts: the CrossCult project, Costas Vassilakis, Angeliki Antoniou, George Lepouras, Manolis Wallace, Ioanna Lykourentzou and Yannick Naudet Proceedings of the second International Conference On Digital Heritage (Euromed2016), 2016.
    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.
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  144. Knowledge-Based Leisure Time Recommendations in Social Networks Dionisis Margaris, Costas Vassilakis, Panagiotis Georgiadis, chapter in: Current Trends on Knowledge-Based Systems: Theory and Applications, to be published in January 2017.
    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.
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  145. Using Social media to stimulate history reflection in cultural heritage Stavroula Bampatzia, Angeliki Antoniou, George Lepouras, Costas Vasilakis and Manolis Wallace, Proceedings of SMAP 2016.
    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.
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  146. Pruning and Aging for User Histories in Collaborative Filtering Dionisis Margaris and Costas Vassilakis, Proceedings of the 2016 IEEE Symposium Series on Computational Intelligence.
    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.
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  147. Serious games: Valuable Tools for Cultural Heritage Stavroula Bampatzia, Ioannis Bourlakos, Angeliki Antoniou, Costas Vassilakis, George Lepouras, Manolis Wallace, Proceedings of the 2016 Games and Learning Alliance Conference 2016.
    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.
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  148. Recommendation Information Diffusion in Social Networks Considering User Influence and Semantics Dionisis Margaris, Costas Vassilakis and Panagiotis Georgiadis, Social Network Analysis and Mining, 6(1), 1-22, Springer, DOI: 10.1007/s13278-016-0416-z, View at Springerlink.
    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.
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  149. Query personalization using social network information and collaborative filtering techniques Dionisis Margaris, Costas Vassilakis and Panagiotis Georgiadis, Future Generation of Computer Systems, Special Issue on Recommender Systems for Large-Scale Social Networks, 2017
    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.
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  150. Improving Collaborative Filtering's Rating Prediction Quality in Dense Datasets, by Pruning Old Ratings Dionisis Margaris and Costas Vassilakis, 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.
    Proceedings of the 22nd IEEE Symposium on Computers and Communications (ISCC17), 2017
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  151. Personalized Augmented Reality Experiences in Museums using Google Cardboards Marinos Theodorakopoulos, Nikos Papageorgopoulos, Andriana Mourti, Angeliki Antoniou, Manolis Wallace, George Lepouras, Costas Vassilakis and Nikos Platis, Proceedings of SMAP 2017, 2017
    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.
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  152. Improving Collaborative Filtering's Rating Prediction Quality by Considering Shifts in Rating Practices Dionisis Margaris and Costas Vassilakis, Proceedings of the 19th IEEE International Conference on business informatics (CBI17), 2017
    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.
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  153. Formalization and visualization of the narrative for museum guides Ioannis Bourlakos, Manolis Wallace, Angeliki Antoniou, Costas Vassilakis, George Lepouras and Anna Vassiliki Karapanagiotou, Proceedings of the third International KEYSTONE Conference, (IKC2017), 2017
    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.
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  154. Enhancing User Rating Database Consistency through Pruning Dionisis Margaris and Costas Vassilakis, to appear in Transactions on Large-Scale Data- and Knowledge-Centered Systems, special issue on Consistency and Inconsistency in Data-centric Applications, Springer
    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 inconsisten-cy 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 be-havior data from the ratings database, which are bound to correspond to invali-dated 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 algo-rithm 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 algo-rithms, which reduce the importance of aged ratings, and a state-of-the-art prun-ing algorithm, using datasets with varying characteristics. It is also validated us-ing two distinct rating prediction computation strategies, namely collaborative fil-tering and matrix factorization. The proposed technique needs no extra infor-mation 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.
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  155. Exploiting Internet of Things Information to Enhance Venues' Recommendation Accuracy Dionisis Margaris and Costas Vassilakis, to appear in Service Oriented Computing and Applications, Springer
    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.
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  156. Stimulation of Reflection and Discussion in Museum Visits through the use of Social Media Costas Vassilakis, Angeliki Antoniou, George Lepouras, Vassilis Poulopoulos, Manolis Wallace, Stavroula Bampatzia and Ioannis Bourlakos, to appear in Social Networks Analysis and Mining, Springer
    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.
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  157. Modeling Server Workloads for Campus Email Traffic Using Recurrent Neural Networks Spyros Boukoros, Anupiya Nugaliyadde, Angelos Marnerides, Costas Vassilakis, Polychronis Koutsakis and Kok Wai Wong Proceedings of the 24th International Conference on Neural Information Processing (ICONIP 2017)
    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.
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  158. Experiences from the development of thematic itineraries in three Greek museums (greek title: "Εμπειρίες από την ανάπτυξη θεματικών διαδρομών σε τρια Ελληνικά μουσεία") A. Antoniou, C. Vassilakis, M. Wallace, G. Lepouraw and V. Poulopoulos, Proceedings of the 2nd PanHellenic conference on Cultural Heritage (Euromed 2017)
    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.
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  159. exhiSTORY: Smart Exhibits That Tell Their Own Stories C. Vassilakis, V. Poulopoulos, A. Antoniou, M. Wallace, G. Lepouras and M. Lopez Nores To appear in Future generation of computer systems
    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.
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