On deadlock-free modular supervisory control of discrete event systems

Discusses the existence of deadlock-free modular supervisors for discrete event systems. By introducing the d-invariant relation between language pairs and supervisor pairs, it is shown that for the case when the control objective is described in terms of a two language intersection, a necessary and sufficient condition for the modular supervisor to be deadlock-free is that the two component subsupervisors are all deadlock-free and this pair of subsupervisors meets a d-invariant relation. For case that the specification is given as a multi-language intersection, the problem remains open