Incremental hierarchical construction of modular supervisors for discrete-event systems

Adoption of the supervisory control framework introduced by Ramadge and Wonham has been slowed somewhat by the problem of state space explosion that arises in systems of the scale common to most industrial applications. Hierarchical and modular approaches have been explored historically as means for addressing this problem. The limitations of these approaches include that a ‘consistent’ hierarchy is often difficult to achieve, and that modular supervisors often conflict with each other when acting in conjunction. This paper offers an approach that addresses some of these issues by incrementally building modular supervisors that are nonconflicting by construction. Abstractions are employed to make the procedure more computationally feasible. Proof is given showing the set of modular supervisors generated in this manner meet given specifications without blocking. Furthermore, examples are provided that demonstrate the reduction in complexity that this approach provides.