On Reachability Analysis of Communicating Finite State Machines

Reachability analysis and the recently proposed reverse reachability analysis are two important verification techniques f o r communicating finite state machines (CFSMs). The issue of the relative eficiency of reachability analysis and reverse reachability analysis is still unsettled. In this paper we f irst propose a new theory of reachability and reverse reachability analysis. Based on the new theory we discuss and analyze suitability of these two reachability analysis methods. W e then present a reachability evaluator, which, given any network of CFSMs, will try to estimate the sizes of the reachable and reverse reachable state spaces b y taking snapshots of the reachability and reverse reachability spaces. The core of the evaluator is the notion of random state generation with seed states, which extends the idea of random state exploration proposed in [Id] . Results f r o m example applications have shown that the evaluator provides an excellent guidance in choosing the better of the two methods.