Guaranteeing Termination of Fully Symbolic Timed Forward Model Checking

Abstract

In this paper we present a normalization technique to guarantee termination of fully symbolic forward model checking for timed automata. Whereas for semi-symbolic model checkers based on convex clock zones there exist methods in the literature to solve this problem, our normalization algorithm can be applied to fully symbolic model checkers representing arbitrary symbolic (convex and non-convex) state sets. Our method is based on a projection of region-equivalent clock valuations to the same area within their equivalence class. In a first approach we present a normalization algorithm for diagonal-free timed automata. Then we generalize the approach to timed automata with diagonal constraints. We show that our normalization technique enables termination of the fixed point iteration in a prototype forward model checker using fully symbolic state set representations.