Relaxed Clock Di erence Diagrams for Timed Automata Model Checking

Clock Di erence Diagrams (CDDs), a BDD-like data structure for model checking of timed automata, were presented in 1999. After the original article the work on them seems to have stopped, although there are still important open questions. The proposed algorithm relied on the traditionally used data structure (DBMs) for most operations. CDDs de nition required that repeated subtrees were aliased, but no clear algorithm was presented for producing such compact representation, which seems costly to achieve. Also, since then, case studies have increased in size. In this article we revisit CDDs by introducing RCDDs, a variation that does not require maximum aliasing. We present the complete set of operations required to perform forward reachability analysis with no need for DBMs. By employing a fully RCDD-based algorithm our experiments show a consistent reduction of time requirements in case studies from the current literature, sometimes up to more than 40%.