Frances L. Johnson and Stuart C. Shapiro
As a knowledge representation and reasoning (KRR) system gathers and reasons about information, it has to update its belief space to maintain consistency. Some belief change operations it can perform include expansion (addition with no consistency checking), contraction (aka removal or retraction), revision (consistent prioritized addition), and consolidation (elimination of any and all inconsistencies). Whether belief change operations are performed on theories or bases, with ideal agents or those that are resource-bounded, there is no doubt that the order of operations typically affects the makeup of the resulting belief base. If a KRR system gains new information that, in hindsight, might have altered the outcome of an earlier belief change decision, the earlier decision should be re-examined. We call this operation reconsideration, and the result is an optimal belief base regardless of the order of previous belief change operations.