Causal Laws and Multi-Valued Fluents

This paper continues the line of work on representing properties of actions in nonmonotonic formalisms that stresses the distinction between being true and beingcaused, as in the system of causal logic introduced by McCain and Turner and in the action languageC proposed by Giunchiglia and Lifschitz. The only fluents directly representable in languageC are truth-valued fluents, which is often inconvenient. We show that both causal logic and languageC can be extended to allow values from arbitrary nonempty sets. Our extension of languageC, calledC+, also makes it possible to describe actions in terms of their attributes, which is important from the perspective of elaboration tolerance. We describe an embedding of C+ in causal theories with multi-valued constants, relate C+ to Pednault’s action language ADL, and show how multi-valued constants can be eliminated in favor of Boolean constants.