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

TL;DR

This paper investigates Zeno-like behaviors in Event Calculus models implemented with goal-directed Answer Set Programming, analyzing their causes, proposing solutions, and developing an automatic detection technique.

Contribution

It systematically studies Zeno-like behaviors in EC models with ASP and introduces methods for their detection and mitigation.

Findings

Identified common EC modeling patterns causing Zeno behaviors

Proposed techniques to address and prevent Zeno-like issues

Developed an automatic detection method for Zeno behaviors

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.