A Model-Based Approach to the Construction of Adaptive Case-Based Planning Systems

1 Chicken and water chestnuts A case-based planner devises new plans by retrieving and adapting old ones from memory (see, e. Ideally, the plan it retrieves from memory should be one that requires the least adaptation to t the current circumstances. Finding this plan in a cost-eeective way is thus a key issue in case-based reasoning (see, e. The approach that is generally taken to this problem is simply to use the goals that the planner is attempting to achieve as indices into its plan library, as exempliied by the CHEF system (Hammond, 1989). In fact CHEF uses not only the goals themselves but also features of those goals that predict interactions that should be avoided. Consider how CHEF uses goals to construct a plan (i.e., recipe) for beef with broccoli by adapting the plan for beef with green beans. The beef with green beans recipe consists essentially of preparing the ingredients, stir-frying the beef with some of the other ingredients , then adding the green beans and stir-frying a bit longer. In order to adapt this recipe to prepare beef with broccoli, CHEF must alter the basic plan outline, introducing a split-and-reform process that avoids an undesirable interaction between the beef, which sweats and produces liquid in the pan when cooked, and broccoli, a crispy vegetable that becomes soggy if cooked in liquid. To avoid this interaction, the broccoli is stir-fried and removed from the pan before the meat and other ingredients are cooked, and then added again just before the dish is nished. When CHEF stores this plan, one of the indices to the plan is that it achieves the goal of avoiding soggy vegetables. At the same time, an anticipation rule is also built so that the planner will generate the goal to avoid soggy vegetables whenever it has the goals to cook a stir-fry dish involving both a meat and a crispy vegetable. Consider now what happens when CHEF is subsequently required to produce a recipe for chicken and snow peas. Because chicken is a meat and snow peas are a crispy vegetable, the anticipation rule acquired earlier generates a goal to avoid soggy vegetables. Using this goal in conjunction with the originally speciied goals, CHEF retrieves the beef and broccoli plan, and adapts it by substituting the required ingredients. The resulting plan includes the split-and-reform process, and it too is indexed under the goal of …