Enhancing Uppaal by Exploiting Symmetry

Efficiency is one of the major concerns in the world of model checking. Consequently, many techniques to optimize the time and space usage of model checking algorithms have been invented. One of these techniques is reduction of the searchable state space through arguments of symmetry. This technique can be very profitable and has been implemented in various model checkers, but not yet in Uppaal, a model checker for timed systems. This paper proposes an enhancement of Uppaal with symmetry reduction. We adopt the theory of symmetry of Ip and Dill and their scalarset data type, as implemented in the model checker Murφ. The main result of this paper is a soundness proof of our symmetry enhancement, which does not follow trivially from the work of Ip and Dill since the description languages of Uppaal and Murφ, which are used to detect the symmetries, are quite different. A secondary result is a proof of the computational difficulty of space-optimal exploitation of full symmetry in a setting with DBM technology.

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