Removing Irrelevant Atomic Formulas for Checking Timed Automata Efficiently

Reachability analysis for timed automata can be done by enumeration of time zones, which are conjunctions of atomic formulas of the form x-y≤(<)n. This paper shows that some of the atomic formulas in a generated time zone can be removed while the reachability analysis algorithm generates the same set of reachable locations. We call such formulas irrelevant ones. By removing the irrelevant formulas, the number of symbolic states associated with each location is reduced. We present two methods to detect irrelevant formulas. Case studies show that, for some kind of timed automata, these methods may significantly reduce the space requirement for reachability analysis.