On Conditional Decomposability

The requirement of a language to be conditionally decomposable is imposed on a specification language in the coordination supervisory control framework of discrete-event systems. In this paper, we present a polynomial-time algorithm for the verification whether a language is conditionally decomposable with respect to given alphabets. Moreover, we also present a polynomial-time algorithm to extend the common alphabet so that the language becomes conditionally decomposable. A relationship of conditional decomposability to nonblockingness of modular discrete-event systems is also discussed in this paper in the general settings. It is shown that conditional decomposability is a weaker condition than nonblockingness.Comment: A few minor correction

Synthesis of Communicating Controllers for Distributed Systems

International audienceWe consider the control of distributed systems composed of subsystems communicating asynchronously; the aim is to build local controllers that restrict the behavior of a distributed system in order to satisfy a global state avoidance property. We model our distributed systems as communicating finite state machines with reliable unbounded FIFO queues between subsystems. Local controllers can only observe their proper local subsystems and do not observe the queues. To refine their control policy, they can use the FIFO queues to communicate by piggybacking extra information to the messages sent by the subsystems. We define synthesis algorithms allowing to compute the local controllers. We explain how we can ensure the termination of this control algorithm by using abstract interpretation techniques, to overapproximate queue contents by regular languages. An implementation of our algorithms provides an empirical evaluation of our method

A constructive and modular approach to decentralized supervisory Control problems

International audienceWe plunge decentralized control problems into modular ones to benefit from the know-how of modular control theory: any decentralized control problem is associated to a natural modular control problem, which over-approximates it. Then, we discuss how a solution of the latter problem delivers a solution of the forme

PSPACE-completeness of Modular Supervisory Control Problems*

In this paper we investigate computational issues associated with the supervision of concurrent processes modeled as modular discrete-event systems. Here, modular discrete-event systems are sets of deterministic finite-state automata whose interaction is modeled by the parallel composition operation. Even with such a simple model process model, we show that in general many problems related to the supervision of these systems are PSPACE-complete. This shows that although there may be space-efficient methods for avoiding the state-explosion problem inherent to concurrent processes, there are most likely no time-efficient solutions that would aid in the study of such “large-scale” systems. We show our results using a reduction from a special class of automata intersection problem introduced here where behavior is assumed to be prefix-closed. We find that deciding if there exists a supervisor for a modular system to achieve a global specification is PSPACE-complete. We also show many verification problems for system supervision are PSPACE-complete, even for prefix-closed cases. Supervisor admissibility and online supervision operations are also discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45090/1/10626_2004_Article_6210.pd

An Efficient Modular Method for the Control of Concurrent Discrete Event Systems: A Language-Based Approach

International audienceIn this paper, we are interested in the control of a particular class of Concurrent Discrete Event Systems defined by a collection of components that interact with each other. We investigate the computation of the supremal controllable language contained in the language of the specification. We do not adopt the decentralized approach. Instead, we have chosen to use a modular centralized approach and to perform the control on some approximations of the plant derived from the behavior of each component. The behavior of these approximations is restricted so that they respect a new language property for discrete event systems called partial controllability condition that depends on the specification. It is shown that, under some assumptions, the intersection of these ``controlled approximations'' corresponds to the supremal controllable language contained in the specification with respect to the plant. This computation is performed without having to build the whole plant, hence avoiding the state space explosion induced by the concurrent nature of the plant. It is finally shown that the class of specifications on which our method can be applied strictly subsumes the class of separable specifications

Une approche modulaire pour le contrôle de systèmes à événements discrets concurrents

National audienceDans cet article, nous nous intéressons au contrôle de systèmes à événements discrets concurrents définis par une collection de sous-systèmes interagissant les uns avec les autres. Étant donné un objectif de contrôle, le but consiste à calculer un superviseur maximal assurant cet objectif, sans construire explicitement le système à contrôler. Des approximations du système G sont dérivés à partir des sous-systèmes qui le composent, et une propriété appelée contrôlabilité partielle, devant être vérifiée par l'objectif sur ces approximations, est introduite. Assurer la contrôlabilité partielle de l'objectif sur chacune des approximations permet, sous certaines hypothèses, d'en déduire un superviseur maximal assurant l'objectif de contrôle sur G. Les calculs effectués ont une faible complexité et ne nécessitent pas de construire explicitement le système G, évitant ainsi l'explosion combinatoire inhérente aux systèmes concurrent