Licentiate thesis 2001-009

Efficient Symbolic State Exploration of Timed Systems: Theory and Implementation

Johan Bengtsson

May 2001


Timing aspects are important for the correctness of safety-critical systems. It is crucial that these aspects are carefully analysed in designing such systems. UPPAAL is a tool designed to automate the analysis process. In UPPAAL, a system under construction is described as a network of timed automata and the desired properties of the system can be specified using a query language. Then UPPAAL can be used to explore the state space of the system description to search for states violating (or satisfying) the properties. If such states are found, the tool provides diagnostic information, in form of executions leading to the states, to help the desginers, for example, to locate bugs in the design.

The major problem for UPPAAL and other tools for timed systems to deal with industrial-size applications is the state space explosion. This thesis studies the sources of the problem and develops techniques for real-time model checkers, such as UPPAAL, to attack the problem. As contributions, we have developed the notion of committed locations to model atomicity and local-time semantics for timed systems to allow partial order reductions, and a number of implementation techniques to reduce time and space consumption in state space exploration. The techniques are studied and compared by case studies. Our experiments demonstrate significant improvements on the performance of UPPAAL.

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