Analysis of distributed multi-periodic systems to achieve consistent data matching

Distributed real-time architecture of an embedded system is often described as a set of communicating components. Such a system is data flow (for its description) and time-triggered (for its execution). This work fits in with these problematics and focuses on the control of the time compatibility of a set of interdependent data used by the system components. The architecture of a component-based system forms a graph of communicating components, where more than one path can link two components. These paths may have different timing characteristics but the flows of information which transit on these paths may need to be adequately matched, so that a component uses inputs which all (directly or indirectly) depend on the same production step. In this paper, we define this temporal data-matching property, we show how to analyze the architecture to detect situations that can cause data matching inconsistencies, and we describe an approach to manage data matching that uses queues to delay too fast paths and timestamps to recognize consistent data

Maximal Group Membership in Ad Hoc Networks

International audienceThe notion of Group communication has long been introduced as a core service of distributed systems. More recently, this notion appeared with a somewhat different meaning in the field of mobile ad hoc systems. In this context, we study the group membership problem. After specifying the basic safety properties of such groups and a maximality criterion based on cliques, we propose a group membership algorithm. Lastly, with respect to this criterion, we compare our algorithm with two group membership algorithms for ad hoc environments. Moreover, a formal description in TLA+ has been programmed and verified by model-checking for small networks

A Data Oriented Approach for Real-Time Systems

International audienceDistributed real-time systems often have to maintain the temporal validity of data. In this paper we present a modelling framework centered on data where a so-called observation relation represents and abstracts the interactions between variables. An observation is a relation between variables, an image and its sources, where the image values depend on past values of the sources. The system architecture is seen as a set of observation relations describing the flow of values between variables. The observation relations are parametrized with timed constraints that limit the time shift between the variables and specify the availability of timely sound values. At this level of abstraction, the designer gives a specification of the system based on timed properties about the timeline of data such as their freshness, latency etc. We proceed to an analysis of the feasibility of such a specification and we formally analyze the correctness of an implementation with respect to a specification. In order to prove the feasibility of an observationbased model, we build a finite state transition system which is bi-similar to the specification. The existence of an infinite execution in this system proves the feasibility of the specification. Possible implementations are described as a set of interacting components which control the flow of values in the system. A finite system is built to prove the correctness of the implementation by model checkin

Supervision de flux pour les contenus hypermédia (optimisation de politiques de préchargement et ordonnancement causal)

L'accès performant aux données multimédia (rapide, cohérent, adapté aux besoins et préférences des utilisateurs et aux ressources disponibles) est un enjeu majeur des recherches actuelles sur le multimédia. Dans le premier volet de cette étude nous proposons de réduire les latences de navigation dans des hypervidéos à l'aide du préchargement. Notre contribution principale est un modèle formel intégrant les habitudes des utilisateurs pour anticiper les interactions futures et décider ce qu'il faut précharger, quand et comment. Ce modèle permet, sous des hypothèses précises, de calculer des politiques optimales de préchargement. La gestion des incertitudes liées au réseau et aux interactions des utilisateurs est un de ses atouts. Notre modèle (un Processus Décisionnel de Markov) et les politiques issues de la résolution sont validés expérimentalement dans une architecture de streaming. Les latences réelles sont cohérentes avec celles prédites par la théorie. Le deuxième volet de ce travail concerne le contrôle de la cohérence de l'accès aux flux multimédia répartis. Nous formalisons les relations entre flux en termes de causalité et introduisons la notion de défilement. Un modèle de calcul réparti est proposé où cette notion remplace la notion d'événement, utilisée classiquement. Nous montrons que le contrôle de ces relations, dans les protocoles de diffusion de groupe, peut être assuré simplement par une datation classique. Dans un deuxième temps, nous modélisons des flux sous forme d'intervalles temporels. Ceci permet de reformuler, à des fins de validation, les relations de causalité entre flux en termes de relations entre intervalles selon l'algèbre de Allen appliquée à un ordre partiel (causal).TOULOUSE-ENSEEIHT (315552331) / SudocSudocFranceF

Mise en oeuvre de tests unitaires dans un contexte de programmation eXtrème répartie

International audienceeXtreme Programming (XP) is a methodology based on principles and practices for quickly developing software. However this approach requires the programmers to be co-located. Many research projects investigate how to extend XP to a distributed environment. However the challenge is to carry out the XP approach without conflicting with the distributed constraints. Our work takes place in this way. More precisely, we propose an extension based on assistance for supporting distributed unit testing, one of the key principles of XP methodology.La programmation eXtrème dite XP (eXtreme Programming) est une méthodologie efficace de développement rapide de logiciels qui exige que les membres d'une équipe de développeurs soient physiquement proches les uns des autres. Des travaux de recherche tentent d'étendre les principes de cette méthodologie à un contexte réparti. Le défi est alors de préserver les qualités fondamentales de l'approche tout en s'affranchissant de la contrainte de proximité physique des développeurs. Notre travail s'inscrit dans cette logique. De façon plus précise, nous proposons de fonder cette extension de XP à un environnement réparti sur l'assistance à la réalisation des tests unitaires, pierre angulaire de la méthodologie XP

Tailoring UNITY to distributed program design

Abstract. As a general framework, UNITY does not offer any specific facility for the design of distributed systems. For such systems, distribution aspects must be represented at a low level, resulting into intricated models and proofs. To provide a more abstract view of distributed systems, we propose two extensions to UNITY. The first one is an observation relation which is integrated in UNITY semantics to provide an abstract communication mechanism. The second one is a mapping operator which accounts for the true parallelism of distributed systems. The paper illustrates, through different examples, how these extensions can be used to help the design of distributed systems in UNITY.