dlm@allegra.UUCP.UUCP (01/22/87)
[Forwarded from the NL-KR Digest.] Title: A Four-Valued Semantics for Terminological Logics Speaker: Peter F. Patel-Schneider Affiliation: Schlumberger Palo Alto Research Date: Monday, February 2, 1987 Location: AT&T Bell Laboratories - Murray Hill 3D-473 Sponsor: Ron Brachman Terminological logics (also called frame-based description languages) are a clarification and formalization of some of the ideas underlying semantic networks and frame-based systems. The fundamental relationship in these logics is whether one concept (frame, class) is more general than (subsumes) another. This relationship forms the basis for important operations, including recognition, classification, and realization, in knowledge representation systems incorporating terminological logics. However, determining subsumption is computationally intractable under the standard semantics for terminological logics, even for languages of very limited expressive power. Several partial solutions to this problem are used in knowledge representation systems, such as NIKL, that incorporate terminological logics, but none of these solutions are satisfactory if the system is to be of general use in representing knowledge. A new solution to this problem is to use a weaker, four-valued semantics for terminological logics, thus legitimizing a smaller set of subsumption relationships. In this way a computationally tractable knowledge representation system incorporating a more expressively powerful terminological logic can be built.