Modeling and Reasoning in Event Calculus Using Goal-Directed Constraint Answer Set Programming

Abstract

Automated commonsense reasoning is essential for building human-like AI systems featuring, for example, explainable AI. Event Calculus (EC) is a family of formalisms that model commonsense reasoning with a sound, logical basis. Previous attempts to mechanize reasoning using EC faced difficulties in the treatment of the continuous change in dense domains (e.g., time and other physical quantities), constraints among variables, default negation, and the uniform application of different inference methods, among others. We propose the use of s(CASP), a query-driven, top-down execution model for Predicate Answer Set Programming with Constraints, to model and reason using EC. We show how EC scenarios can be naturally and directly encoded in s(CASP) and how its expressiveness makes it possible to perform deductive and abductive reasoning tasks in domains featuring, for example, constraints involving dense time and fluents.

ASP for Flexible Payroll Management

“…We implement the FEC axioms in ASP in the same way as [9] and use the clingo system recommended in [7]. Recently, the goal-directed ASP system s(CASP) [13] was also used to implement the event calculus formalism and reason about events without grounding the whole ASP program [1]. However, since the task we try to solve explicitly requires us to consider the state of the employee at each timepoint, we would not benefit from such an approach.…”

Knowledge-Assisted Reasoning of Model-Augmented System Requirements with Event Calculus and Goal-Directed Answer Set Programming

“…For example, we assume the following initial state of the system and compute when the alerts will be raised (initiallyP(F) means that initially fluent F is true and initiallyN(F) means initially fluent F is false). The fluent start is used to define the rate of change of barometric altitude as an event calculus trajectory 3 .…”

“…Our work builds upon recent advances made within the s(CASP) system [2], a query-driven (or goal-directed) implementation of predicate ASP that supports constraint solving over reals, permitting the faithful representation of time as a continuous quantity. The s(CASP) system permits the modeling of event calculus directly [3]. An advantage of using the event calculus-in contrast to automata and Kripke structure-based approaches-is that it can directly model cyber-physical systems, thereby avoiding "pollution" due to (often premature) design decisions that must be made otherwise.…”