Proceedings of the Annual Meeting of the Cognitive Science Society

Re-uting plans that were created for one situation to solve a new problem is often more efficient than creating a new plan from scratch (e.g., [Fikes et al, 1972] and [Carbonell, 1986]. However,a plan that was created for one problem may not exactly fit a new situation; in that case, itwill have to be modified. There are two major problenu with re-using plans: (1) decidingwhether to modify a plan, use it as is, or discard it; and (2) modifying the plan efficiently.Our solution to these problems is to store information with plan preconditions to guide theplanner during plan application. Our approach is novel in two ways. First, we have identifieda type of precondition, called a Bexible precondition, that has information associated with itthat helps the planner decide whether or not to modify the plan should the precondition beviolated. Second, our preconditions contain information (derived from past experience usingthe plan) that provides heuristics for chioiging the plan so that the offending preconditionis either no longer violated or no longer necessary. By using this approach, otir planner canquickly determine whether or not to modify a plan, then efficiently perform the modification.Our work is implemented in the Consumer-Advisor System (CAS) [Kolodner and Cullingford,1986; Turner, 1986; Turner, in press], a common-sense advice-giving program.