Showing papers by "Jean-François Raskin published in 2002"

A Comparison of Control Problems for Timed and Hybrid Systems

Abstract: In the literature, we find several formulations of the control problem for timed and hybrid systems. We argue that formulations where a controller can cause an action at any point in dense (rational or real) time are problematic, by presenting an example where the controller must act faster and faster, yet causes no Zeno effects (say, the control actions are at times 0, 1/2, 1, 1 1/4, 2, 2 1/8, 3, 3 1/16, . . . ). Such a controller is, of course, not implementable in software. Such controllers are avoided by formulations where the controller can cause actions only at discrete (integer) points in time. While the resulting control problem is well-understood if the time unit, or "sampling rate" of the controller, is fixed a priori, we define a novel, stronger formulation: the discrete-time control problem with unknown sampling rate asks if a sampling controller exists for some sampling rate. We prove that this problem is undecidable even in the special case of timed automata.

Towards the Automated Verification of Multithreaded Java Programs

Abstract: In this paper we investigate the possible application of parameterized verification techniques to synchronization skeletons of multithreaded Java programs. As conceptual contribution, we identify a class of infinite-state abstract models, called Multi-Transfer Nets (MTNs), that preserve the main features of the semantics of concurrent Java. We achieve this goal by exploiting an interesting connection with the Broadcast Protocols of [7], and by introducing the notion of asynchronous rendez-vous. As technical contribution, we extend the symbolic verification techniques of [6] based on Covering Sharing Trees and structural invariants to MTNs. As practical contribution, we report on experimental results for verification of examples of multithreaded Java programs.

Game analysis of abuse-free contract signing

Abstract: In this paper we report on the verification of two contract signing protocols. Our verification method is based on the idea of modeling those protocols as games, and reasoning about their properties as strategies for players. We use the formal model of alternating transition systems to represent the protocols and alternating-time temporal logic to specify properties. The paper focuses on the verification of abuse-freeness, relates this property to the balance property, previously studied using two other formalisms, shows some ambiguities in the definition of abuse-freeness and proposes a new, stronger definition. Formal methods are not only useful here to verify automatically the protocols but also to better understand their requirements (balance and abuse-freeness are quite complicated and subtle properties).

Monotonic Extensions of Petri Nets: Forward and Backward Search Revisited.

Abstract: In this paper, we revisit the forward and backward approaches to the verification of extensions of infinite state Petri Nets. As contributions, we propose an efficient data structure to represent infinite downward closed sets of markings and to compute symbolically the minimal coverability set of Petri Nets, we identify a subclass of Transfer Nets for which the forward approach generalizes and we propose a general strategy to use both the forward and the backward approach for the efficient verification of general Transfer Nets.