John D. Garofalakis

Integrating GIS, GPS and GSM technologies for the effective management of ambulances

In this paper, we describe a system offering a solution to the problem of ambulance management and emergency incident handling in the prefecture of Attica in Greece. It is based on the integration of geographic information system (GIS), global positioning system (GPS) and global system for mobile communication (GSM) technologies. The design of the system was the result of a project funded by the Greek Secretariat of Research and Technology. A significant operation for the handling of emergency incidents is the routing of ambulances to incident sites and then to the closest appropriate hospitals. The response time of a real-time system like ours to such queries is of vital significance. By using efficient data structures for the implementation of the graph representing the road network, the time performance of the shortest-path algorithm can be enhanced. Incorporating the efficient algorithm within the GIS will increase our systems viability.

Web site optimization using page popularity

Awkward arrangement of documents in an HTML tree can discourage users from staying at a Web site. The authors have developed an algorithm for dynamically altering the organization of pages at sites where the main design objective is to give users fast access to requested data. The algorithm reads information from the HTTP log file and computes the relative popularity of pages within the site. Based on popularity (defined as a relationship between number of accesses, time spent, and location of the page), the hierarchical relationships between pages are rearranged to maximize accessibility for popular pages.

A Web-Based Intelligent Tutoring System Using Hybrid Rules as Its Representational Basis

In this paper, we present the architecture and describe the functionality of a Web-based Intelligent Tutoring System (ITS), which uses neurules for knowledge representation. Neurules are a type of hybrid rules integrating symbolic rules with neurocomputing. The use of neurules as the knowledge representation basis of the ITS results in a number of advantages. Part of the functionality of the ITS is controlled by a neurule-based inference engine. Apart from that, the system consists of four other components: the domain knowledge, containing the structure of the domain and the educational content, the user modeling component, which records information concerning the user, the pedagogical model, which encompasses knowledge regarding the various pedagogical decisions, and the supervisor unit that controls the functionality of the whole system. The system focuses on teaching Internet technologies.

Use of RSS feeds for content adaptation in mobile web browsing

While mobile phones are becoming more popular, wireless communication vendors and device manufacturers are seeking new applications for their products. Access to the large corpus of Internet information is a very prominent field, however the technical limitations of mobile devices pose many challenges. Browsing the Internet using a mobile phone is a large scientific and cultural challenge. Web content must be adapted before it can be accessed by a mobile browser. In this work we build on the proxy server solution to present a new technique that uses Really Simple Syndication (RSS) feeds for the adaptation of web content for use in mobile phones. This technique is based in concrete design guidelines and supports different viewing modes. Experimentation shows a significant decrease in the transformed content of about 80% in size facilitating cost-effective web browsing.

An Analytical Performance Model for Multistage Interconnection Networks with Blocking

Multistage Interconnection Networks (MINs) allow efficient communication between network components and also among the components of parallel systems. This paper presents an approximate performance model for self routing multistage interconnection networks, applied for 2 x 2 switches which are subject to blocking situations when the packets compete for a full output port of a next stage switch. We apply our model to variable network size MINs and we study the performance under different traffic conditions. In our approximation the bulk of packets that arrive in each cycle to the MIN inputs, follow a Bernoulli distribution. We derive an approximate formula for the utilization of each queue and based on this, we approximate the blocking behavior (probabilities) and the steady-state distributions of populations for each queue of the MIN. This novel analytical model is validated by extensive simulations. Our analytical method gives more accurate results than previous existing analytical models and converges very fast.

Efficient web-based open and distance learning services

Abstract In this paper, we present data management issues faced during the design and development of an open distance learning system for the University of Patras, Greece. In order to handle data efficiently, as required in a web tele-training application, for each type of information maintained, different strategies must be deployed according to their behaviour and structure. The diversity and complexity of data, the network aspect of the application and web deficiencies impose an architecture design incorporating a plethora of technologies and tools that must be integrated in such a fashion that they efficiently organise these data preserving their relationships. This presents a software engineering challenge requiring coherence of solutions at all levels: structures, consistency, security, models, and protocols. The paper presents the data components of an open and distance learning (ODL) system that access the information stored in a database and the file system, their underlying technology, their interaction with the network services, and features regarding the ways they address issues faced in an open vendor-independent distance learning environment and outlines the systems overall architecture. In addition, this paper presents the architecture, the design and the services of a network-based information system that supports open and distance learning activities. The open and distance learning information system (ODLIS) offers synchronous and asynchronous distance learning and management of information system (MIS) services to support the educational procedure. The ODLIS is a web-based application, which runs over the Internet using real time protocols.

An analytical performance model for multistage interconnection networks with finite, infinite and zero length buffers

Abstract Multistage Interconnection Networks (MINs) with crossbar switches have been used to interconnect processors and memory modules in parallel multiprocessor systems. They also play an increasingly important role in the development of Asynchronous Transfer Mode (ATM) networks. In this paper we analyze the general case of MINs, made of k × k switches with finite, infinite or zero length buffers (unbuffered). The exact solution of the steady-state distribution of the first stage is derived for all cases. We use this to get an approximation for the steady-state distributions in the second stage and beyond. In the case of unbuffered switches we reach the known exact solution for all the stages of the MIN. Our results are validated by extensive simulations.

Queueing delays in buffered multistage interconnection networks

Our work deals with the analysis of the queueing delays of buffered multistage Banyan networks of multiprocessors. We provide tight upper bounds on the mean delays of the second stage and beyond, in the case of infinite buffers. Our results are validated by simulations performed on a network simulator constructed by us. The analytic work for network stages beyond the first, provides a partial answer to open problems posed by previous research.

Hierarchical Itemspace Rank

Sparsity is an innate characteristic of recommender system databases and it is known to present one of the most challenging difficulties collaborative filtering methods have to deal with. In this paper, we propose Hierarchical Itemspace Rank (HIR); a novel recommendation algorithm that exploits the intrinsic hierarchical structure of the itemspace to tackle this problem, and to alleviate the related limitations it imposes to the quality of recommendation. A comprehensive set of experiments on the MovieLens100K, the MovieLens1M and the Yahoo!R2Music datasets indicates that our method is very effective in handling sparsity, even in its most extreme manifestation - the cold-start problem. Our tests show that HIR outperforms several state-of-the-art recommendation algorithms in widely used metrics, having at the same time the advantage of being computationally efficient and easily implementable.

Mechanisms and analysis for supporting multicast traffic by using multilayer multistage interconnection networks

Multilayer multistage interconnection networks (MLMINs) integrate communication with network components and the components of parallel systems, especially when they service multicast traffic. This paper presents an approximate performance methodology for self-routing MLMINs that consist of two segments, each of which is composed of symmetrical switch elements. The first segment is subject to blocking situations with one mode of packet transmission policy (unicast). The second segment--the multilayer--is blocking free and employs double modes of transmission policy (unicast and multicast replication). Applying the current analytical model, which is based on a convergence method on the above types of MLMINs, an estimate can be made of their performance indicators. This model was applied to variable network size MLMINs under different multicasting patterns of traffic. It was also validated by extensive simulations. All the MLMINs under study apply special packet (traffic) management techniques, which allow for the integration of sub-networking into larger networks such as grids. The results are accurate and useful for network engineering, especially in the service of local area networks.