DECISION-PROBLEMS FOR INTERACTING FINITE STATE MACHINES

Given a system of n interacting finite state machines (FSM's) and a state configuration, the reachability problem is to examine whether this configuration is reachable within the system. We investigate the complexity of this decision problem and three of its derivatives, namely 1) verifying system determinism, 2) testing for the existence of unspecified inputs to any FSM within the system, and 3) testing for the exclusiveness of two intra-FSM signals. We prove that these problems are ail PSPACE-complete. We show the effect of these problems on the state assignment process for concurrent systems of interacting FSM's.