Modelling and Verification of Timed Systems with the Event Calculus and s(CASP)

We model the well-known Train-Gate-Controller (railroad crossing problem) system in Event Calculus using Goal-Direct Answer Programming realized via the s(CASP) system. Our paper illustrates the ease with which such a cyber-physical system’s requirements specification is modeled and its properties verified relative to prior assumptions. Event calculus allows for succinct modeling of a dynamic system due to the near-zero semantic gap between the system’s requirements specification and their event calculus encoding. This is to be distinguished from automata-theoretic approaches which have to explicitly encode the notion of state and define explicit transitions between states. Further, Event Calculus is naturally expressed in s(CASP) without need for discretization of continuous physical quantities including time. This is due to the goal-direct answer set semantics of s(CASP) combined with constraint solving over reals. Continuous properties require no discretization unlike other approaches to model Event Calculus in SAT-based Answer Set solvers.

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