dlm@allegra.CSNET (06/26/87)
Date: Thursday, July 2
Time: 2:00 PM
Place: AT&T Bell Laboratories MH 3D-473
David S. Touretzky
Computer Science Department
Carnegie Mellon University
A Clash of Intuitions: The Current State of
Nonmonotonic Multiple Inheritance Systems
Early attempts at combining multiple inheritance with nonmonotonic reasoning
were based on straightforward extensions to tree-structured inheritance
systems, and were theoretically unsound. In The Mathematics of Inheritance
Systems, or TMOIS, I described two basic problems that these systems cannot
handle. One involves reasoning with true but redundant assertions; the other
involves ambiguity.
TMOIS provided the definition and analysis of a theoretically sound multiple
inheritance system, accompanied by inference algorithms. Other definitions for
inheritance have since been proposed by Sandewall and by Horty, Thomason, and
Touretzky that are equally sound and intuitive, but do not always agree with
the system defined in TMOIS. At the heart of the controversy is a clash of
intuitions about certain fundamental issues such as skepticism versus
credulity, the direction in which inheritance paths are extended, and classical
versus intuitive notions of consistency. In this talk I will catalog the
issues, map out a design space, and describe interesting properties that result
from certain choices of definitions. Just as there are alternative logics,
there may be no single ``best'' approach to nonmonotonic multiple inheritance.
This is joint work with Richmond Thomason of the University of Pittsburgh and
John Horty of CMU.
Sponsor: Ron Brachman