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Demie journée Thématique: Modélisation

ppeterlo — 2010-03-12T08:10:25Z

Exposé Elie Najm (ENST)

lhelouet — 2010-03-01T13:24:16Z

Exposé T. Chatain (LSV)

lhelouet — 2010-02-16T16:28:39Z

Concurrent semantics of real-time distributed systems

Techniques that aim at improving reliability and safety of automated systems have dramatically improved during the last twenty years (synthesis, model-checking, test...) Studying a complex system generally requires the use of multiple techniques and tools. Consequently the system must be modeled in different formalisms. The difficulty is to convince one that that the multiple representations are equivalent. For instance, considering two popular formalisms for real-time distributed systems, we would like to be able to transform a time Petri net into a network of timed automata. But we require that this transformation preserves concurrency. Yet the first works about formal comparisons of the expressivity of these models do not consider preservation of concurrency. Here we formalize model transformations that preserve not only the timed sequential behavior, but also concurrency. The notion of preservation of concurrency will be formalized using a concurrent semantics based on partial orders.

Exposé Tayssir Touili (LIAFA)

lhelouet — 2010-03-01T13:23:38Z

Reachability Analysis of Networks of Communicating Pushdown Systems

We address the verification problem of networks of communicating pushdown systems modeling communicating parallel programs with procedure calls. Processes in such networks can read the control state of the other processes according to a given communication structure (specifying the observability rights between processes). The reachability problem of such models is undecidable in general. First, we prove that it becomes decidable for networks with acyclic communication structure. Then, we define a class of networks that effectively preserves recognizability (hence, its reachability problem is decidable). Next, we consider networks where the communication structure can change dynamically during the execution according to a phase graph. The reachability problem for these dynamic networks being undecidable in general, we consider reachability when the switches in the communication structures are bounded. We show that this problem is undecidable even for one switch. Then, we define a natural class of models for which this problem is decidable. This class can be used in the definition of an efficient semi-decision procedure for the analysis of the general model of dynamic networks. Our techniques allowed to find bugs in two versions of a Windows NT Bluetooth driver. This is joint work with Faouzi Atig and Ahmed Bouajjani.