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Institute
This paper gives a short overview of a model checking tool for real-time systems. The modeling language are timed automata extended with concepts for modular modeling. The tool provides reachability analysis and refinement checking, both implemented using the data structure BDD. Good variable orderings for the BDDs are computed from the modular structure of the model and an estimate of the BDD size. This leads to a significant performance improvement compared to the tool RED and the BDD-based version of Kronos.
In this paper we analyze the efficiency of binary decision diagrams (BDDs) and clock difference diagrams (CDDs) in the verification of timed automata. Therefore we present analytical and empirical complexity results for three communication protocols. The contributions of the analyses are: Firstly, they show that BDDs and CDDs of polynomial size exist for the reachability sets of the three protocols. This is the first evidence that CDDs can grow only polynomially for models with non-trivial state space explosion. Secondly, they show that CDD-based tools, which currently use at least exponential space for two of the protocols, will only find polynomial-size CDDs if they use better variable orders, as the BDD-based tool Rabbit does. Finally, they give insight into the dependency of the BDD and CDD size on properties of the model, in particular the number of automata and the magnitude of the clock values.