A General Architecture for Decentralized Supervisory Control of Discrete-Event Systems

We consider a generalized form of the conventional decentralized control architecture for discrete-event systems where the control actions of a set of supervisors can bè`fused'' using both union and intersection of enabled events. Namely, the supervisors agree a priori on choosing``fusion by union'' for certain controllable events and``fusion by intersection'' for certain other controllable events. We show that under this architecture, a larger class of languages can be achieved than before since a relaxed version of the notion of co-observability appears in the necessary and suf®cient conditions for the existence of supervisors. The computational complexity of verifying these new conditions is studied. A method of partitioning the controllable events between``fusion by union'' and``fusion by intersection'' is presented. The algebraic properties of co-observability in the context of this architecture are presented. We show that appropriate combinations of fusion rules with corresponding decoupled local decision rules guarantee the safety of the closed-loop behavior with respect to a given speci®cation that is not co-observable. We characterize an``optimal'' combination of fusion rules among those combinations guaranteeing the safety of the closed-loop behavior. In addition, a simple supervisor synthesis technique generating the in®mal pre®x-closed controllable and co-observable superlanguage is presented.