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 be "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 sufficient 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 specification 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 infimal prefix-closed controllable and co-observable superlanguage is presented.