On Zeno-like Behaviors in the Event Calculus with Goal-directed Answer Set Programming

Abstract: It has been argued that Event Calculus (EC) is suitable for modeling high-level specifications of safety-critical cyber-physical systems. The primary advantage lies in the rather small semantic gap between EC models and requirements expressed in a semi-formal natural language. Moreover, its use of continuous time and variables avoids imprecision that stems from discretization. In the past, we have shown that a goal-directed ASP system can be used for implementing these EC models. However, precise representation of time as an infinitesimally divisible continuous quantity leads to Zeno-like behaviors and to non-termination in such a system. In this work, we model a number of well-known example problems from the literature to systematically study various natural EC modeling patterns that yield these Zeno-like behaviors, and propose ways to deal with them. Moreover, we also propose a technique to automatically detect all such cases.