Representation of supervisory controls using state tree structures, binary decision diagrams, automata, and supervisor reduction

In the synthesis of an optimal nonblocking supervisor for a discrete-event system (DES), the problem of state explosion is a well-known computational obstacle. This problem can often be managed successfully by the use of state-tree structures (STS) and binary decision diagrams (BDD). Unfortunately BDD control functions may become quite large, and as such difficult to represent and interpret. In some cases it may, therefore, be convenient to convert an STS/BDD based controller to automaton form, and then apply a well known algorithm for supervisor reduction. In this paper we illustrate the advantage of this approach with a concrete example.