Proceedings of the Annual Meeting of the Cognitive Science Society

We examine how acting in dynamic, complex, not entirely predictable environments affects the indexing, storage and reuieval of cases in a memory-based system. W e discuss how a hierarchical goal sUiicture can be exploited to provide indices for searching and storage when planning and acting in everyday environments under time pressure. The tradeoffs between the costs and utility associated with attempting to prevent repeating a failure or missing an opportunity are briefly examined. Considering these tradeoffs leads to distinguishing between when failures can be allowed to recur and when they should be anticipated and avoided. The amount of effort expended when handling failures differs for the two situations, but in both cases a hierarchical goal structure can be used to choose effective indices efficiently. This paper describes the approach taken in our EXPEDITER^ system and briefly compares it to other approaches.