Report Number: CS-TR-90-1312
Institution: Stanford University, Department of Computer Science
Title: A validation structure based theory of plan modification and reuse
Author: Kambhampati, Subbarao
Author: Hendler, James A.
Date: June 1990
Abstract: A framework for the flexible and conservative modification of plans enables a planner to modify its plans in response to incremental changes in their specifications, to reuse its existing plans in new problem situations, and to efficiently replan in response to execution time failures. We present a theory of plan modification applicable to hierarchical nonlinear planning. Our theory utilizes the validation structure of stored plans to yield a flexible and conservative plan modification framework. The validation structure, which constitutes a hierarchical explanation of correctness of the plan with respect to the planner's own knowledge of the domain, is annotated on the plan as a by-product of initial planning. Plan modification is formalized as a process of removing inconsistencies in the validation structure of a plan when it is being reused in a new (changed) planning situation. The repair of these inconsistencies involves removing unnecessary parts of the plan and adding new non-primitive tasks to the plan to establish missing or failing validations. The resultant partially reduced plan (with a consistent validation structure) is sent to the planner for complete reduction. We discuss the development of this theory in the PRIAR system, present an empirical evaluation of this theory, and characterize its completeness, coverage, efficiency and limitations.