Situation Calculus by Term Rewriting

TL;DR

This paper introduces a novel approach to the situation calculus by representing situations as first-order terms and using rewrite rules for actions, enabling efficient planning and flexible modeling.

Contribution

It presents a flexible, term-based representation of situations and actions in the situation calculus, enhancing previous models with subterm operations and bidirectional rewrite rules.

Findings

Efficient planning via rewrite rule completion methods.

Flexible modeling of actions affecting subsets of fluents.

Comparison showing advantages over the fluent calculus.

Abstract

A version of the situation calculus in which situations are represented as first-order terms is presented. Fluents can be computed from the term structure, and actions on the situations correspond to rewrite rules on the terms. Actions that only depend on or influence a subset of the fluents can be described as rewrite rules that operate on subterms of the terms in some cases. If actions are bidirectional then efficient completion methods can be used to solve planning problems. This representation for situations and actions is most similar to the fluent calculus of Thielscher \cite{Thielscher98}, except that this representation is more flexible and more use is made of the subterm structure. Some examples are given, and a few general methods for constructing such sets of rewrite rules are presented. This paper was submitted to FSCD 2020 on December 23, 2019.