Unfoldings for Message Passing Timed Automata

In this thesis we develop a state space reduction technique for networks of timed automata based on unfoldings to alleviate the state space explosion problem due to concurrently enabled actions. For the purpose of verifying a system, standard model checking techniques construct its sequential state space that su ers an exponential growth when applied to distributed systems because of concurrently enabled, independent actions: during the construction of the state space these actions are ordered arbitrarily to simulate concurrency in the sequential model. For untimed systems, state space reduction techniques like stubborn sets that omit the construction of redundant information, and unfoldings that represent concurrent events in a partial order have successfully been applied to alleviate the exponential growth. These techniques apply a simple syntactical criterion to identify independent actions. This criterion is not applicable to networks of timed automata as simple examples show, which renders the existing techniques unapplicable. But networks of timed automata face the state space explosion problem as well which raises the demand for a speci c reduction technique for these systems. In this thesis, we consider a special, but practically relevant class of networks of timed automata as a formal model for discrete, distributed, timed systems. We develop a novel technique that constructs a complete, nite representation of such a system's state space. This representation is the complete, nite pre x of an unfolding in which concurrently enabled actions are partially ordered. We show that this technique is capable of reducing the size of the state space by magnitude. We are presently not aware of any state space reduction technique for timed automata with similar results.