Discrete and continuous strategies for timed-arc Petri net games

Abstract

Automatic strategy synthesis for a given control objective can be used to generate correct-by-construction controllers of real-time reactive systems. The existing symbolic approach for continuous timed game is a computationally hard task and current tools like UPPAAL TiGa often scale poorly with the model complexity. We suggest an explicit approach for strategy synthesis in the discrete-time setting and show that even for systems with closed guards, the existence of a safety discrete-time strategy does not imply the existence of a safety continuous-time strategy and vice versa. Nevertheless, we prove that the answers to the existence of discrete-time and continuous-time safety strategies coincide on a practically motivated subclass of urgent controllers that either react immediately after receiving an environmental input or wait with the decision until a next event is triggered by the environment. We then develop an on-the-fly synthesis algorithm for discrete timed-arc Petri net games. The algorithm is implemented in our tool TAPAAL, and based on the experimental evidence, we discuss the advantages of our approach compared to the symbolic continuous-time techniques.