In SOA environments, as the number of published Web Services grows, the provision of a robust, scalable and efficient discovery service is still an unresolved issue. In this paper we present a P2P-based infrastructure that leverages the semantic technologies to support a scalable and accurate service discovery process. The key concept of the presented idea is the creation of an overlay network organized in several semantic groups of peers, each specialized in answering queries pertaining to specific applicative domains. Groups are formed by clustering together peers offering services that are semantically related. A semantic query routing mechanism ensures the delivery of queries to the groups that are semantically "worth" to respond. In this paper the architecture details of the proposed solution is presented. A system prototype has also been implemented and validated through a case study deployed on the PlanetLab testbed.

Semantic web services have recently appeared as an enabling technology for the challenging task of automated service discovery and composition. In addition, the growing number of web services demands for distributed discovery mechanisms which do not suffer of the scalability problems of the centralized ones. A framework based on the P2P paradigm to enhance the service discovery process has been designed: it is mainly based on the grouping of peers which are semantically "close" to each other. In this paper, we focus on the semantic characterization of a peer, which is built by taking into account the set of services it provides. In order to reach an high level of service integration, our framework builds an abstract "expertise" of the peer, which is independent of the specific semantic language used to annotate the service.

Grid systems are becoming the underlying infrastructure for many high-performance distributed scientific applications. Resources in these systems have heterogeneous features, are connected by potentially unreliable networks, and are often under different administrative management domains. These remarks show how a new generation of techniques, mechanisms and tools need to be considered that can cope with the complexity of such systems and provide the performance suitable for scientific computing applications. In this paper an architecture for monitoring services in Grid environments based on mobile agent technology is presented. One of the most interesting aspects of the proposed approach is the possibility of customizing the parameters to be monitored. After describing the general framework where agents will execute, an application for improving the capabilities of traditional network monitoring paradigms is presented.

In this paper we present a new real-time algorithm for object tracking by on-line video analysis. This algorithm is able to track an object even in presence of substantial perspective transformations and to detect changes in the object shape due to changes in its structure. The core of the system is a chain made of autonomous software agents (MOVels), which acts like an active contour on the sequence of frames.

In this paper we propose an edge-based segmentation algorithm built on a new type of active contour which is fast, has a low computational complexity and does not introduce unwanted smoothing on the retrieved contours. The contours are always returned as closed chains of points, resulting in a very useful base for subsequent shape representation techniques.

In this paper a prototype of a distributed video-on-demand server is presented. The technical aspects regarding the realization of this kind of service provider are dealt with, paying particular attention to exploiting the architecture the system is based on. The proposed system easily allows, in any broadband local network environment, the realization of a low-cost/high-performance distributed video server, through the clustering of the local workstations. The system has been implemented and tested, and the results of its performance and scalability are presented in the final sections of this paper.

We have developed a fast method to segment 2-D grey-level images, obtaining closed-line, continuous, smooth and analytical representations of object contours. The results are very good, even in presence of noisy or low contrast images, and the shape of objects are retrieved with very good accuracy.

We concentrate on the architectural issues of parallelizing I/O access in a disk array system by means of definition of a new, particularly flexible architecture, called partial dynamic declustering, which is fault-tolerant and offers higher levels of performance and reliability than the solutions normally used. A simulation analysis highlights the efficiency of the proposed solution in balancing the file system workload and demonstrates its validity in both cases of unbalanced loads and expansion of the system. Particular attention is also paid to the definition of analytical models, based on stochastic reward nets, in order to analyze the performance and reliability of the system. The response time distribution function is evaluated and a specific performance analysis with varying degrees of declustering and workload is carried out.>

Continuous monitoring of a computer network performance is probably the only solution which allows prompt identification of anomalous functioning conditions and knowledge of parameters on which to base speedy, effective recovery interventions. A number of tools for performance management already exist, but their effectiveness is limited as they are essentially inserted inside owner network management solutions. In the paper we describe the realization of PMt, a platform for the development of performance management applications for the control and real-time management of a heterogeneous computer network. PMt imposes an object-oriented view of the distributed system, defines a performance management design methodology which adapts well to really distributed system management and provides the user with a set of tools and services to assist him both in the design of new performance management applications and in actual management of the whole system.>

With a view to improving the performance and the fault tolerance of mass storage units, this paper concentrates on the architectural issues of parallelizing I/O access and a disk array system by means of definition of a new, particularly flexible architecture, called Partial Dynamic Declustering, which is fault-tolerant and offers higher levels of performance and reliability than the solutions normally used. A fast distributed algorithm based on a dynamic structure and usable for the implementation of an efficient I/O subsystem manager is proposed. Particular attention is also paid to the definition of analytical models based on Stochastic Reward Petri nets in order to analyze the performance and reliability of the system proposed.>

In this paper we present a design for a general-purpose fuzzy processor, the core of which is based on an analog-numerical approach combining the inherent advantages of analog and digital implementations, above all as regards noise margins. The architectural model proposed was chosen in such a way as to obtain a processor capable of working with a considerable degree of parallelism. The internal structure of the processor is organized as a cascade of pipeline stages which perform parallel execution of the processes into which each inference can be decomposed. A particular feature of the project is the definition of a 'fuzzy-gate', which executes elementary fuzzy computations, on which construction of the whole core of the processor is based. Designed using CMOS technology, the core can be integrated into a single chip and can easily be extended. The performance obtainable, in the order of 50 Mega fuzzy rules per second, is of a considerable level.>

The paper provides a systematic approach to modelling and assessing gracefully degrading systems, exploiting the formalism offered by Petri Nets. The procedure followed is based on the definition of some fundamental modules, the composition of which allows a complete model of the system to be obtained. The model can then be solved by computer simulation or analytically by means of a class of Petri Nets to obtain interesting performance parameters. The paper examines a number of real cases and describes the results obtained.

The bandwidth balancing method (BBM) introduced into the latest versions of the DQDB protocol is discussed. An extended analysis is presented of the behavior of the protocol with the BBM incorporated, assuming that more than one priority level is active in the network. The results are oriented towards evaluation of the effect the BBM has on access delay and bandwidth sharing in overload conditions.>

This paper describes considerations for potential future public data communication services interconnecting users on private local area networks belonging to different administrative domains. The relevant management issues are addressed in an architecture consisting of distributed software modules organized in a hierarchical structure supporting network administration functions. The authors describe an experimental internetworking unit being built to explore the functional capabilities needed to interface ethernet networks to systems operating at OC-3 SONET/SDH rates of 155.22 Mb/s with basic asynchronous transfer mode (ATM) transport capabilities. They describe bandwidth allocation, address screening, address translation, and traffic monitoring service aspects in the experimental prototype.>

Topics related to the service quality of a network made up of interconnected LANs are discussed. As the size of a network increases, so do reconfiguration times, thus reducing service availability, increasing frame loss, and leading to performance degradation. This degradation may be substantial if circumstances requiring reconfiguration occur frequently. Two types of networks are compared by assessing the parameters which directly affect the quality of service of the network. The first uses media access control (MAC) bridges based on the standard spanning tree algorithm; the second uses parallel MAC bridges, by means of which the network can be organized into islands, thus making reconfiguration selective. In both cases the bridged LAN is modeled according to the schemes suggested by systems reliability theory, which allows assessment of performance parameters directly affecting service quality, such as the mean time to failure (MTTF), performability, and availability.>

The authors analyze error-recovery mechanisms in local area networks (LANs) with token-ring access with particular reference to the problem of ring failure, i.e. (breaks in the ring or transmitter and/or receiver failure). They also suggest solutions to increase fault tolerance. The solutions suggested concern both the architecture (topology) and the access protocol (medium access control). In particular, a process capable of performing automatic network reconfiguration is proposed. The process is first described functionally and then specified through the finite-state machine.>