Enhancing the Inverse Method with State Merging

Keeping the state space small is essential when verifying realtime systems using Timed Automata (TA). In the model-checker Uppaal, the merging operation has been used extensively in order to reduce the number of states. Actually, Uppaal’s merging technique applies within the more general setting of Parametric Timed Automata (PTA). The Inverse Method (IM ) for a PTA A is a procedure that synthesizes a zone around a given point π (parameter valuation) over which A is guaranteed to behave in an equivalent time-abstract manner. We show that the integration of merging into IM leads to the synthesis of larger zones around π. It also often improves the performance of IM , both in terms of computational space and time, as shown by our experimental results.