[mod.ai] Seminar - A Four-Valued Semantics for Terminological Logics

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.