ADVANCED PLAN-GENERATING SYSTEMS

This chapter discusses two systems that can deal with interacting goals in a more sophisticated manner than STRIPS and various hierarchical methods for plan generation. RSTRIPS is a modification of STRIPS that uses a goal regression mechanism for circumventing goal interaction problems. A typical use of this mechanism prevents RSTRIPS from applying an F -rule, F1 , that would interfere with an achieved precondition, P , needed by another F-rule, F2 , occurring later in the plan. Because F2 occurs later than F1 , it must be that F2 has some additional unachieved precondition, P ′ that led to the need to apply F1 first. Instead of applying F1 , RSTRIPS rearranges the plan by regressing F through the F -rule that achieves P . Now, the achievement of the regressed P ′ will no longer interfere with P . Some of the techniques and conventions used by RSTRIPS can best be introduced while discussing an example problem in which the goals do not happen to interact.