Abstract.A state/event model is a concurrent version of Mealy machines used for describing embedded reactive systems. This paper introduces a technique that uses compositionality and dependency analysis to significantly improve the efficiency of symbolic model checking of state/event models. This technique makes possible automated verification of large industrial designs with the use of only modest resources (less than one hour on a standard PC for a model with 1421 concurrent machines). The results of the paper are being implemented in the next version of the commercial tool visualSTATE TM.
We investigate techniques for verifying hierarchical systems, i.e., finite state systems with a nesting capability. The straightforward way of analysing a hierarchical system is to first flatten it into an equivalent non-hierarchical system and then apply existing finite state system verification techniques. Though conceptually simple, flattening is severely punished by the hierarchical depth of a system. To alleviate this problem, we develop a technique that exploits the hierarchical structure to reuse earlier reachability checks of superstates to conclude reachability of substates. We combine the reusability technique with the successful compositional technique of [13] and investigate the combination experimentally on industrial systems and hierarchical systems generated according to our expectations to real systems. The experimental results are very encouraging: whereas a flattening approach degrades in performance with an increase in the hierarchical depth (even when applying the technique of [13]), the new approach proves not only insensitive to the hierarchical depth, but even leads to improved performance as the depth increases.
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