Distributed and web-based systems

Publications on distributed, web- and semantics-based systems

Distributed systems

Publications on distributed systems

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.

Note: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.
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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.

Note: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.
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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

Note: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.
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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.

Note: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.
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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.

Note: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.
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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.

Note: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.
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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.

Note: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.
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Improving Performance of Finite-buffered Blocking Delta Networks with 2-class Priority Routing by 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.

Note: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.
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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.

Note: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.
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PDF icon IJITS-tr.pdf300.24 KB
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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
International Journal of Parallel, Emergent and Distributed Systems, Vol. 26, No. 5, October 2011, 381–397, 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.

Note: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.
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Performance Analysis of Dual-Priority Multilayer Multistage Interconnection Networks under Multicast Environment

D. C. Vasiliadis, G. E. Rizos, C. Vassilakis,
Journal of Networks, June 2011

Abstract
Next-generation network architectures strive to achieve high bandwidth and ultralow latency for the packets traversing the offered end-to-end paths. Multistage Interconnection Networks (MINs) are often employed for implementing NGNs, but while MINs are fairly flexible in handling varieties of traffic loads, they tend to quickly saturate under broadcast and multicast traffic, especially at increasing size networks. As a response to this issue, multilayer MINs have been proposed, however their performance prediction and evaluation has not been studied sufficiently insofar. In this paper, we evaluate and discuss the performance of multilayer MINs under multicast traffic, considering also two levels of packet priorities, since support for multiple QoS levels is an indispensible requirement for NGNs. Different offered loads and buffer size configurations are examined in this context, and performance results are given for the two most important network performance factors, namely packet throughput and delay. We also introduce and calculate a universal performance fac¬tor, which includes the importance aspect of each of the above main performance factors. The findings of this study can be used by NGN system designers in order to predict the performance of each configuration and adjust the design of their communication infrastructure to the traffic requirements at hand.

Note: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.
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PDF icon paper_multicast_priority-tr.pdf441.73 KB
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Performance Analysis of Multi-Layered Multi-Priority Asymetric-Sized Delta Networks

D. C. Vasiliadis, G. E. Rizos, C. Vassilakis
Journal of Computer Systems, 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.

Note: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.
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PDF icon min-ml-mp-asym.pdf487.79 KB
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Performance Analysis of Multistage Interconnection Networks determining optimal parameters for data-intensive business applications

D.C. Vasiliadis, G.E. Rizos, and C. Vassilakis
Proceedings of the 7th IBIMA Conference.

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.

Note: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.
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Performance Analysis of dual priority single-buffered blocking Multistage Interconnection Networks

D. C. Vasiliadis , G. E. Rizos , C. Vassilakis
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.

Note: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.
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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.

Note: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.
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PDF icon Two_priority_MINs.pdf262.18 KB
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Performance Evaluation of Distance Vector Routing Protocol on a Wireless Circular Model

D. C. Vasiliadis, G. E. Rizos, C. Vassilakis
Proceedings of 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.

Note: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.
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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)

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.

Note: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.
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Performance Study of Multi-Layered Multistage Interconnection Networks under Hotspot Traffic Conditions

D. C. Vasiliadis, G. E. Rizos, C. Vassilakis
Journal of Computer Systems, Networks, and Communications, (to appear), 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.

Note: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.
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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.

Note: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.
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PDF icon PQ-CBWFQ-WRR-MIN-v3i.pdf534.53 KB
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Performance analysis of blocking banyan switches

D.C. Vasiliadis, G.E. Rizos, and C. Vassilakis
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.

Note: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.
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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

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.

Note: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.
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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.

Note: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.
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PDF icon c063.pdf289.15 KB
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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.

Note: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.
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PDF icon ICCMSE2007_1501.pdf338.39 KB
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Service-Oriented Architectures

Publications on Service Oriented Architectures

A Collaborative Filtering Algorithm with Clustering for Personalized Web Service Selection in Business Processes

Dionisis Margaris, Panayiotis Georgiadis and 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.

Note: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.
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Year: 

A Hybrid Framework for WS-BPEL Scenario Execution Adaptation, Using Monitoring and Feedback Data

Dionisis Margaris, Costas Vassilakis, and Panayiotis 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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Year: 

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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Year: 

Adapting WS-BPEL scenario execution using collaborative filtering techniques

Dionisis Margaris, Panayiotis Georgiadis and Costas Vassilakis
Proceedings of IEEE RCIS 2013

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.

Note: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.
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An Active Blackboard for Service Discovery, Composition and Execution

George Lepouras, Costas Vassilakis, Anya Sotiropoulou, Dimitrios Theotokis, Akrivi Katifori
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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An Active Ontology-based Blackboard Architecture for Web Service Interoperability

George Lepouras, Costas Vassilakis, Anya Sotiropoulou, Dimitrios Theotokis, Akrivi Katifori
Proceedings o f the Second IEEE Conference on Service Systems and Service Management, 2005.

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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Year: 

An integrated framework for QoS-based adaptation and exception resolution in WS-BPEL scenarios

Dionisis Margaris, Costas Vassilakis, and Panayiotis Georgiadis
Proceedings of ACM SAC 2013

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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An integrated framework for adapting WS-BPEL scenario execution using QoS and collaborative filtering techniques

Dionisis Margaris, Costas Vassilakis, Panayiotis Georgiadis
Science of Computer Programming 98(2015) 707–734, Elsevier

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.

Note: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder. The paper is available through ScienceDirect
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Year: 

Combining Quality of Service-based and Collaborating filtering-based techniques for BPEL scenario execution adaptation

Dionisis Margaris, Panayiotis Georgiadis and Costas Vassilakis
Technical report SDBS-TR-14002

Abstract:
In this technical report we give examples on how Quality of Service-based and Collaborating filtering-based techniques can be combined to drive the adaptation of WS-BPEL scenario execution.

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PDF icon sdbs-tr-14-002-v3.pdf546.12 KB
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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.

Note: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.
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PDF icon enhancing-BPEL-scenarios.pdf248.59 KB
Year: 

Exception Resolution for BPEL Processes: a Middleware-based 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.

Article available through the ACM Author-izer service:

ACM DL Author-ize serviceException resolution for BPEL processes: a middleware-based framework and performance evaluation
Kareliotis Christos, Costas Vassilakis, Efstathios Rouvas, Panayiotis Georgiadis
iiWAS '08 Proceedings of the 10th International Conference on Information Integration and Web-based Applications & Services, 2008

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Year: 

Improving QoS Delivered by WS-BPEL Scenario Adaptation through Service Execution Parallelization

Dionisis Margaris, Costas Vassilakis, and Panayiotis Georgiadis
Proceedings of ACM SAC 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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Year: 

On Replacement Service Selection in WS-BPEL Scenario Adaptation

Dionisis Margaris, Panayiotis Georgiadis and 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.

Note: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.
Year: 

Preprocessor transformations for implementing greedy and service provider-level QoS-based adaptation for BPEL scenario execution

Kareliotis, Costas Vassilakis, Efstathios Rouvas, Panayiotis Georgiadis
SDBS Lab technical report, August 2012

Abstract:
In this technical report, we describe and exemplify the transformations applied by the WS-BPEL preprocessor, in order to produce a BPEL scenario that can be adapted according to QoS specifications, in the architecture described in [1]. [1] adopts a greedy algorithm for performing adaptation, i.e. it uses only the QoS specifications pertaining to the first invoke activity IA to a specific service provider S, so as to decide the service provider to which both IA and further invocations to operations provided by S will be directed. The greedy algorithm may result in suboptimal bindings, while in some cases it may even lead to situations where the middleware is unable to find any appropriate service selection for fully servicing the BPEL scenario, albeit such a path does exist. To this end, a service provider-level adaptation strategy can be employed: the transformed scenario may communicate to the ASOB middleware [1] the information concerning all operation invocations to a specific partner link before the first invocation an operation provided by the specific partner link is executed, and therefore the ASOB middleware can exploit this information to remedy the problems stemming from the greedy nature of the adaptation method specified in [1].

Year: 

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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Year: 

QoS-Driven Adaptation of BPEL Scenario Execution

Chris Kareliotis, 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.

Note: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.
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Year: 

QoS-aware Exception Resolution for BPEL Processes: A Middleware-based Framework and Performance Evaluation

Kareliotis Christos, Costas Vassilakis, Efstathios Rouvas, Panayiotis Georgiadis
International Journal on Web and Grid Services (IJWGS), 2009 - Vol. 5, No.3 pp. 284 - 320

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 consumer-specified 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.

Note: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.
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Year: 

Towards Dynamic, Relevance-Driven Exception Resolution in Composite Web Services

Kareliotis Christos, Vassilakis Costas, Georgiadis Panagiotis
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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Year: 

Web Service Execution Streamlining

Costas Vassilakis, George Lepouras, Akrivi Katifori
Proceedings of the the Third IEEE Conference on Service Systems and Service Management - ICSSSM 06, 2006.

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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Year: 

Web Systems

Publications on Web Systems

A Web Browser for ISDN Card Phones

Dimitris Maroulis, Sotiris Aronis, Vassiliki Nassiopoulou, Nikos Grammenos, Costas Vassilakis
Journal of Internet Technology, Journal of Internet Technology, vol 5, no 3, 2004.

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.

Note: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.
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PDF icon mini-browser-f.pdf141.52 KB
Year: 
Research area: 

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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PDF icon support-lifelong-learning.pdf295.59 KB
Year: 
Research area: 

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.

Note: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.
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PDF icon museums2-tr.pdf341.22 KB
Research area: 

Content enrichment through dynamic annotation

George Weir, George Lepouras, Costas Vassilakis
Proceedings of the 6th International Conference on Enterprise Information Systems, ICES 04, 2004

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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PDF icon contentenrichment-paper.pdf1.17 MB
Year: 
Research area: 

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.

Note: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.
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Year: 
Research area: 

Is Server-Side Programming Killing Your Web Server?

C. Vassilakis, G. Lepouras
Poster presentation in ActiveWeb 99, 1999.

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.

Note: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.
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PDF icon ActiveWebPaper.pdf135.59 KB
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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, 2000.

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.

Note: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.
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PDF icon ml-web-site.pdf134.82 KB
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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.

Note: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.
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PDF icon serving-enhanced-hypermedia.pdf401.76 KB
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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.

Note: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.
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PDF icon wiki-technical-report.pdf506.43 KB
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