Professor John McCarthy
Father of AI


Actions and Other Events in Situation Calculus

This is a new (2001 August) article on situation calculus. It differs from previous approaches in three ways. It distinguishes internal events that happen spontaneously from external events (actions). It also treats processes, e.g. a buzzer, that do not settle down. The non-monotonic reasoning is circumscription done situation by situation.

This article presents a situation calculus formalism featuring events as primary and the usual actions as a special case. Events that are not actions are called internal events and actions are called external events. The effects of both kinds of events are given by effect axioms of the usual kind. The actions are assumed to be performed by an agent as is usual in situation calculus. An internal event e occurs in situations satisfying an occurrence assertion for that event.

A formalism involving actions and internal events describes what happens in the world more naturally than the usual formulations involving only actions supplemented by state constraints. Ours uses only ordinary logic without special causal implications. It also seems to be more elaboration tolerant.

The article appeared in the KR2002 Proceedings.

Download the article in PDF.