Search

In scientic computing, systems often manage computations that require continuous acquisition of of satellite data and the management of large databases, as well as the execution of analysis software and simulation models (e.g. Monte Carlo or molecular dynamics cell simulations) which may require several weeks of continuous run. These systems, consequently, should ensure the continuity of operation even in case of serious faults. HAVmS (High Availability Virtual machine System) is a highly available, "fault tolerant" system with zero downtime in case of fault. It is based on the use of Virtual Machines and implemented by two servers with similar characteristics. HAVmS, thanks to the developed software solutions, is unique in its kind since it automatically failbacks once faults have been fixed. The system has been designed to be used both with professional or inexpensive hardware and supports the simultaneous execution of multiple services such as: web, mail, computing and administrative services, uninterrupted computing, data base management. Finally the system is cost effective adopting exclusively open source solutions, is easily manageable and for general use.

In this paper we deal with the problem of designing virtual path layouts in ATM networks when the hop-count is given and the load has to be minimized. We first prove a lower bound for networks with arbitrary topology and arbitrary set of connection requests. This result is then applied to derive lower bounds for the following settings: (i) one-to-all (one node has to be connected to all other nodes of the network) in arbitrary networks; (ii) all-to-all (each node has to be connected to all other nodes in the network) in several classes of networks, including planar and k-separable networks and networks of bounded genus. We finally study the all-to-all setting on two-dimensional meshes and we design a virtual path layout for this problem. When the hop-count and the network degree are bounded by constants, our results show that the upper bounds proposed in this paper for the one-to-all problem in arbitrary networks and for the all-to-all problem in two-dimensional mesh networks are asymptotically optimal. Moreover, the general lower bound shows that the algorithm proposed in Gerstel (Ph.D. Thesis, Technion-Haifa, Israel, 1995) for the all-to-all problem in k-separable networks is also asymptotically optimal. The upper bound for mesh networks also shows that the lower bound presented in this paper for the all-to-all problem in planar networks is asymptotically tight.

In this paper we introduce a new quick-find data structure to represent disjoint sets, called binomial list, showing that it has a better single-operation worst case time complexity than any previously known approach in solving the set union and intersection problem, a variant of the classical disjoint set union problem.

Freshness of information in real-time search is central in social networks, news, blogs and micro-blogs. Nevertheless, there is not a clear experimental evidence that shows what principled approach effectively combines time and content. We introduce a novel approach to model freshness using a survival analysis of relevance over time. In such models, freshness is measured by the tail probability of relevance over time. We also assume that the probability distributions for freshness are heavy-tailed. The heavy-tailed models of fresh-ness are shown to be highly effective on the micro-blogging test collection of TREC 2011. The improvements over the stateof-the-art time-based models are statistically significant or moderately significant.

Fast packet switches based on banyan interconnection networks and their variations are being proposed for Broadband Integrated Services Digital Network (B-ISDN). Previous analyses on buffered banyan networks mainly assume the store-and-forward operation of the switching systems. In this paper we study the effect of cut-through switching on buffered banyan networks. Two types of buffered banyan networks are considered: those with the switching elements employing input buffers and those employing output buffers. We extend the analytical method of Theimer et al. to multibuffered banyan networks, and to buffered banyan networks with output buffering in the switching elements. We present the analyses of buffered banyan networks operating under cut-through switching. The results of these analyses confirm the simulation results, originally made by Bubenik and Turner, that cut-through switching in buffered banyan networks improves both throughput and delay performances.

In this paper, we introduce a supervised method for the generation of a dictionary of weighted opinion bearing terms from a collection of opinionated documents. We also describe how such a dictionary is used in the framework of an algorithm for opinion retrieval, that is for the problem of identifying the documents in a collection where some opinion is expressed with respect to a given query topic. Several experiments, performed on the TREC Blog collection, are reported together with their results; in these experiments, the use of different combinations of DFR (Divergence from Randomness) probabilistic models to assign weights to terms in the dictionary and to documents is studied and evaluated. The results show the stability of the method and its practical utility. Moreover, we investigate the composition of the generated lexicons, mainly focusing on the presence of stop-words. Quite surprisingly, the best performing dictionaries show a predominant presence of stop-words. Finally, we study the effectiveness of the same approach to generate dictionaries of polarity-bearing terms: preliminary results are provided.

Due to the complexity of topical opinion retrieval systems, standard measures, such as MAP or precision, do not fully succeed in assessing their performances. In this paper we introduce an evaluation framework based on artificially defined opinion classifiers. Using a Monte Carlo sampling, we perturb a relevance ranking by the outcomes of these classifiers and analyse how the opinion retrieval performance changes. In this way it is possible to assess the performance of an approach to opinion mining from that of the overall system and to clarify how relevance and opinion are affected by each other.

We investigate the effectiveness of both the standard evaluation measures and the opinion component for topical opinion retrieval. We analyze how relevance is affected by opinions by perturbing relevance ranking by the outcomes of opinion-only classifiers built by Monte Carlo sampling. Topical opinion rankings are obtained by either re-ranking or filtering the documents of a first-pass retrieval of topic relevance. The proposed approach establishes the correlation between the accuracy and the precision of the classifier and the performance of the topical opinion retrieval. Among other results, it is possible to assess the effectiveness of the opinion component by comparing the effectiveness of the relevance baseline with the topical opinion ranking.

We study the evaluation of opinion retrieval systems. Opinion retrieval is a relatively new research area, nevertheless classical evaluation measures, those adopted for ad hoc retrieval, such as MAP, precision at 10 etc., were used to assess the quality of rankings. In this paper we investigate the effectiveness of these standard evaluation measures for topical opinion retrieval. In doing this we split the opinion dimension from the relevance one and use opinion classffiers, with varying accuracy, to analyse how opinion retrieval performance changes by perturbing the outcomes of the opinion classiffiers. Classiffiers could be studied in two modalities, that is either to re-rank or to filter out directly documents obtained through a first relevance retrieval. In this paper we formally outline both approaches, while for now focussing on the filtering process. The proposed approach aims to establish the correlation between the accuracy of the classiffiers and the performance of the topical opinion retrieval. In this way it will be possible to assess the effectiveness of the opinion component by comparing the effectiveness of the relevance baseline with that of the topical opinion.

We present a method to automatically generate a term-opinion lexicon. We also weight these lexicon terms and use them at real time to boost the ranking with opinionated-content documents. We define very simple models both for opinion-term extraction and document ranking. Both the lexicon model and retrieval model are assessed. To evaluate the quality of the lexicon we compare performance with a well-established manually generated opinion-term dictionary. We evaluate the effectiveness of the term-opinion lexicon using the opinion task evaluation data of the TREC 2007 blog track.

Une extrusion du probleme de l'Union des ensembles est consideree, ou il est possible d'effectuer une recherche de l'histoire de la partition. Introduction d'une structure de donnees partiellement persistante qui maintient une partition d'un ensemble de n elements sans aucun cout additionnel, meme dans le cas de la complexite de la structure ephemere

An extended distribution of computations for multi threading Java applications, requires an extended communication infrastructure. Since large scientific communities wish to adopt the Java paradigm as basis language for their resource-consuming and space-consuming algorithms, then wide JVM computational farms represent an important goal. We propose an interesting experiment, called JASMINA, concerning the deploying of JVMs instances on JXTA platform. JASMINA purposes is to show the first attempt to discover, aggregating and manage a wide JVM farms over JXTA platform. We discuss about the adopted embedding of JXTA paradigm into JVM architecture, and we show some observed behaviours from the effects of JXTA properties on the execution and distribution of Java applications

This paper defines the main logical functionalities and the software architecture of a framework that overcomes the limits of UDDI in fully exploiting the advantages offered by dynamic binding. The framework, relying on the services offered by remote monitoring agents, makes it possible for UDDI Registries to associate a value of convenience to different implementations of the same tModel. This value will lead Service Requestors in the choice of implementations to be contacted and invoked. UDDI Registries with this enhanced behavior still expose an interface compliant to the standard UDDI specification, thus being fully and transparently integrable in the UDDI infrastruc ture. The framework fills the gap existing between approaches to the discovery of Web Services that do not deal with any aspect of their performance and more complex solutions that guarantee a certain level of quality in providing services. This paper also describes the main design and implementation issues concerning a first open source Java prototype of the framework.

Given a minimum spanning tree of a 2-node connected, real weighted, planar graph G = (V, E) with n nodes, we study the problem of finding, for every node v ∈ V, a minimum spanning tree of the graph G - v (the graph G deprived of v and all its incident edges). We show that this problem can be solved on a pointer machine in optimal linear time, thus improving the previous known O(n ċ α(n, n)) time bound holding for general sparse graphs, where α is the functional inverse of Ackermann's function. In this way, we obtain the same runtime as for the edge removal version of the problem, thus filling the previously existing gap. Our algorithm finds application in maintaining wireless networks undergoing transient station failures.

The use of a mobile code, partly interpreted language such as Java is investigated as a tool to build highly portable implementations of multimedia communication protocols. In particular, we concentrate on the implementation of the real-time protocol and focus our attention on three main issues: first, we evaluate the quality and accuracy of the services offered by some relevant primitive operations as they are provided on different Java platforms; second, we concentrate on a suitable object-oriented design which makes RTP functionalities both well-integrated and easily accessible; finally, we perform an overall evaluation of the efficiency of the proposed implementation both in terms of resulting packet loss and delay jitter.

This paper mainly concerns with the design and the performance evaluation of network systems offering a high quality, high reliable videoconferencing service to a community of users dispersed on a metropolitan area. A network topology has been considered in which Ethernet technology based LAN segments are interconnected by a triangular ATM backbone. The main issues of interest in the paper are: the selection and the evaluation of meaningful indices of user satisfaction; the efficiency of Ethernet technology based LAN segments in supporting the real time transmission of multimedia flows; the dimensioning of ATM virtual channels established on a single link; the potentiality of IP and ATM integrated architectures in maintaining the quality of multimedia interactive services in the presence of link fault conditions. Several series of simulations have been performed dealing with different topological configurations, numbers of simultaneously active videoconference sessions, users locations and temporal sequences of activation of the traffic generators. The quality of the user perception has been evaluated with respect to different simulation scenarios. The simulation results show that the ATM technology is a very satisfactory solution to legacy LANs internetworking. ATM link fault tolerance is reached, in a transparent way, simply rerouting ATM switched virtual channels on the available links.

Given a communication network undergoing a transient component failure, a swap algorithm provides the maintenance of the network functionality by means of a minimum number of adjustments. Swap algorithms have recently received growing attention for managing transient failures in classic wired networks, due to their practical usefulness. In this paper, we propose efficient swap algorithms to guarantee survivability in a linear radio communication network undergoing transient station failures. More precisely, given an optimal range assignment for a set of n stations with bases spread on a line, and a bounded number of hops h, we show that, as a consequence of a single non-base station failure, the network survivability can always be guaranteed through a minimum number of adjustments, i.e., by updating either of one station in O(hlogn) time, or two stations in O(n) time, or three stations in O(hn) time, all using O(n) space, depending on the structure of the network around the failed station. Furthermore, our swap algorithms identifies the best network reconfiguration in terms of the additional required power.

In this paper we present the Netlab Quality Management Framework (NQMF), a set of tools especially designed to support controlled experimental analysis of voice-over IP (Internet Protocol) implementations. NQMF implements an integrated methodology to generate, in a controlled way, packet loss and delay sequences which effectively reproduce the fluctuating conditions of the Internet, and especially the high-frequency phenomena that mainly influence speech intelligibility. Our generator is based on a large set of measured sample traces, recorded in a variety of conditions over the network, and takes into special account the so-called 'coffee break' peaks. We also discuss a validation procedure that we carried out to account for the improvement that our generator has over simpler ones already proposed in the literature.

In this paper a framework for the subjective assessment of the quality of perception and interaction of audio communications over not guaranteed QoS IP networks, is defined and validated. One of the most significant components of such framework is a low cost network performance modeling system. The validation process mainly consisted in proving that the user level of satisfaction, as measured in the framework, is strictly related to the network performances. With this aim, several series of tests have been prepared and completed, according to the ITU-T recommendations for the subjective performance assessment , using different audio conference tools and modeling different network traffic conditions.

In this paper, the use of a mobile code, partly interpreted language, such as Java, is investigated as a tool to build highly portable implementations of multimedia real time applications. In particular, we concentrate on the implementation of an audio-conference tool. First, we evaluate the efficiency of some Java implemented basic functionality in the real time processing of audio flows. Second, we produce a suitable object oriented design of the tool. Third, the tool has been entirely implemented in Java, with the only exception of some specific audio devices drivers. Finally, we evaluate the tool implementation effectiveness. The obtained results affirm the potentiality of Java in the design and the implementation of real time multimedia applications.

In this paper a new data structure is introduced for the efficient on-line insertion of a sequence S of keys into a dictionary. The data structure takes advantage by the presence in S of subsets of adjacent keys which maintain their adjacency in the dictionary too, supporting the insertion of t keys in O(plog s + (t - p)) worst case time and O (s) worst case space, where s is the size of the dictionary and p is the number of such subsets. Some applications, as specified in the paper, specifically require for this property.

In this paper we propose an alternative approaches for the efficient solution of the set union and intersection problem, a variant of the classical disjoint set union problem, in which two distinct sequences of unions are simultaneously performed on two distinct collections of n singletons. In this context, it makes sense to introduce a new operation, named findint(x), that, given an element x, returns the intersection of the two sets containing x in both collections. We use a new data structures called intersection lists that reaches the optimal Θ(p) worst case time for executing a findint operation, where p is the size of the output, and spends O(n) worst case time for a union and O(1) worst case time for a find operation.

We consider the problem of deriving good approximations of the convex hull of a set of points in the plane in the realistic case that only arbitrary finite approximations of the real valued coordinates can be known. In particular, the algorithm we introduce derives sequences of improved certified approximations converging to the exact solution, at the same time allowing the insertion of new points to the problem instance. The complexity analysis of the algorithm is performed by referring to a suitable computation model, based on a RAM with logarithmic costs, and the derived space and time bounds are shown to be competitive with respect to current off-line algorithms.