CHEF: A Model of Case-Based Planning

Case-based planning is based on the idea that a machine planner should make use of its own past experience in developing new plans, relying on its memories instead of a base of rules. Memories of past successes are accessed and modified to create new plans. Memories of past failures are used to warn the planner of impending problems and memories of past repairs are called upon to tell the planner how to deal with them. Successful plans are stored in memory, indexed by the goals they satisfy and the problems they avoid. Failures are also stored, indexed by the features in the world that predict them. By storing failures as well as successes, the planner is able to anticipate and avoid future plan failures. These ideas of memory, learning and planning are implemented in the case-based planner CHEF, which creates new plans in the domain of Szechwan cooking. I WHAT IS CASE-BASED PLANNING? Case-based planning is planning from experience. A case-based planner differs sharply from planners that make use of libraries of goals and plans in that it relies on an episodic memory of past planning experiences. As a result, memory organization, indexing, plan modification, and learning are central issues in case-based planning. Because this sort of planner has to be able to reuse the plans that it builds, it must be able to understand and explain why the plans that it has built succeed or fail in order to properly store them for later use. This means that a cased-based planner not only needs to have a powerful memory organization, it must also have a strong model of the causality of the domain in which it operates. The case-based approach to planning is to treat planning tasks as memory problems. Instead of building up new plans from scratch, A case-based planner recalls and modifies past plans. Instead of seeing plan failures as planning problems alone, it treats them as expectation failures that indicate a need to modify its understanding of the world. And instead of treating plans as disposable items that are used once and then forgotten, a case-based planner treats them as valuable commodities that can be stored and recalled for later use. In general, a case-based planner treats at the problem of building and maintaining plans as an interaction between its knowledge base and the world. Any problem that arises out of a disparity between what the planner knows and what is requires that it alter not only its plan but also the expectations that led to the creation of that plan.