Verification Methods for the Divergent Runs of Clock Systems

Abstract

We present a methodology for proving temporal properties of the divergent runs of reactive systems with real-valued clocks. A run diverges if time advances beyond any bound. Since the divergent runs of a system may satisfy liveness properties that are not satisfied by some convergent runs, the standard proof rules are incomplete if only divergent runs are considered. First, we develop a sound and complete proof calculus for divergence, which is based on translating clock systems into discrete systems. Then, we show that simpler proofs can be obtained for stronger divergence assumptions, such as unknown epsilon-divergence, which requires that all delays have a minimum duration of some unknown constant epsilon. We classify all real-time systems into an infinite hierarchy, according to how well they admit the translation of eventuality properties into equivalent safety properties.