A New Approach to Upward-Closed Set Backward Reachability Analysis

In this paper we present a new framework for computing the backward reachability from an upward-closed set in a class of parameterized (i.e. infinite state) systems that includes broadcast protocols and petri nets. In contrast to the standard approach, which performs a single least fixpoint computation, we consecutively compute the finite state least fixpoint for constituents of increasing size, which allows us to employ binary decision diagram (BDD)-based symbolic model checking. In support of this framework, we prove necessary and sufficient conditions for convergence and intersection with the initial states, and provide an algorithm that uses BDDs as the underlying data structure. We give experimental results that demonstrate the existence of a petri net for which our algorithm is an order of magnitude faster than the standard approach, and speculate properties that might suggest which approach to apply.