Representing Actions in Default Logic : A Situation

We address the problem of representing common-sense knowledge about action domains in the formalism of default logic. We employ a methodology proposed by Gelfond and Lifschitz which involves rst deening a high-level language for representing knowledge about actions, and then specifying a translation from the high-level action language into a general-purpose formalism, such as default logic. Accordingly, we deene a high-level action language AC, and specify sound and complete translations of portions of AC into default logic. The language AC includes propositions that represent \static causal laws" of the following kind: a uent formula can be made true by making a uent formula true. Such propositions are more expressive than the state constraints traditionally used to represent background knowledge. Our translation of AC domain descriptions into default logic is simple, in part because the \rule-like" nature of causal laws is easily reeected in such a rule-based formalism.