AI.THROOP@R20.UTEXAS.EDU (David Throop) (07/11/86)
CIRCULAR-REASONER: A Knowledge-Representation Tool for Couches The classic question "How long will it take my brother-in-law and his friend Larry to get the couch from the living room, around a tight corner and into the guest bedroom?" has inspired several advances in AI knowledge representation. The spatial and temporal aspects of the problem have proved particularly difficult. Early work in logic representations was able to show that (Couch X) could be unified with (Furniture X) and push the intractable aspects back a level of abstraction. Rule based systems were able to diagnose Larry's wrenched back after the first attempt, and show that if anybody ever solved the intractable spatial problems, they should leave the answer in the knowledge base. Frame based systems showed that intractable problems could be pushed back a further level through inheritance. Causal reasoning systems can reason about all of the possible behaviors of the couch as it undergoes the process of being shoved around the corner, and move the temporal and spatial questions back into a meta-knowledge-base. I propose to generalize these methods for pushing back hard problems. In particular the program CIRCULAR-REASONER represents these four knowledge representation systems as a linked list. This linked list can be NCONCed to itself so that each level, another representation is just around the corner. Spatial and temporal aspects can be handled by routines that access this list recursively, so that hard problems can be sent away and never come back. David Throop -------