Change, Change, Change: Three Approaches

Abstract

We consider the frame problem, that is, characterizing the assumption that properties tend to persist over time . We show that there are at l east three distinct assumptions that can be made. We show the first assumption, which have been widely studied, is not naturally captured by circumscription. The first assumption is, "there is as little change as possible between one situation and the next". This is closely related to temporal projection. The second assumption is that actions have as few e ffe cts as possible. This has arisen in causal approaches. We show this assumption cannot be captured by any circumscription policy, as it compares models with differ ent domains. We consider a third assumption - there are as many frame axioms true as possibl e-w hich can be capt ured by circumscription. All three assumptions differ, which we show by giving examples. All agree on a small class of theories , those axiomatized by effect axioms and a class of sentences we call compatible binary domain constraints. Further, for a similar class of theories a deduction theorem holds , allowing observations, or facts about particular situations, to be brought through the non-monotonic consequence relation. This justifies approaches based on separating "observations" from "e ffects", and applying projection to the effects, to solve problems based on causality reasoning.