ylfink@water.waterloo.edu (ylfink) (01/21/88)
DEPARTMENT OF COMPUTER SCIENCE
UNIVERSITY OF WATERLOO
SEMINAR ACTIVITIES
ARTIFICIAL INTELLIGENCE SEMINAR
- Thursday, January 28, 1988
Dr. Peter F. Patel-Schneider of Schlumberger Palo Alto
Research, will speak on ``A Four-Valued Semantics for
Terminological Logics''.
TIME: 3:30 PM
ROOM: MC 3003
ABSTRACT
Terminological logics formalize and extend the notions
of concepts, roles, and restrictions present in
semantic networks, frame-based systems, and object-
oriented programming systems. The most important
semantic relationship in these logics is subsumption--
-whether a concept is more general than another.
Subsumption is a non-trivial relationship and if the
terminological logic is expressively powerful, then
determining whether one concept subsumes another is
computationally intractable. Because of this
intractability, knowledge representation systems based
on terminological logics are not suitable for use in
knowledge-based systems.
This problem can be solved by using a four-valued
semantics, resulting in an expressively powerful
terminological logic which has tractable subsumption.
The subsumptions supported by the logic are a type of
``structural'' subsumption, where each structural
component of one concept must have an analogue in the
other concept. Structural subsumption captures an
important set of subsumptions, similar to the
subsumptions computed in KL-ONE and NIKL. The four-
valued semantics can thus be used to develop object-
based knowledge representation systems suitable for use
in knowledge-based systems.