Improved BDD-Based Discrete Analysis of Timed Systems

Model checking timed systems through digitization is relatively easy, compared to zone-based approaches. The applicability of digitization, however, is limited mainly for two reasons, i.e., it is only sound for closed timed systems; and clock ticks cause state space explosion. The former is mild as many practical systems are subject to digitization. It has been shown that BDD-based techniques can be used to tackle the latter to some extent. In this work, we significantly improve the existing approaches by keeping the ticks simple in the BDD encoding. Taking advantage of the ‘simple’ nature of clock ticks, we fine-tune the encoding of ticks and are able to verify systems with many ticks. Furthermore, we develop a BDD library which supports not only encoding/verifying of timed state machines (through digitization) but also composing timed components using a rich set of composition functions. The usefulness and scalability of the library are demonstrated by supporting two languages, i.e., closed timed automata and Stateful Timed CSP.