clarke@utcsri.UUCP (Jim Clarke) (02/23/87)
No title and abstract were available when this talk was first announced:
---------------------------------
A.I. SEMINAR, Tuesday, March 3, 3 p.m., GB 120:
An Approach to Default Reasoning Based on a First-Order Conditional Logic
James P. Delgrande
School of Computing Science,
Simon Fraser University,
Burnaby, B.C., Canada V5A 1S6
This talk describes an approach to default reasoning. The approach is based on
an extension to classical first-order logic wherein the logic is augmented with
a "variable conditional" operator for representing default statements. Truth
in the resulting logic is based on a possible worlds semantics: the default
statement alpha => beta is true just when beta is true in the most uniform
worlds in which alpha is true. Inferences of default properties of individuals
rely on two assumptions: first that the world being modelled by a set of
sentences is as uniform as consistently possible and, second, that sentences
that may consistently be assumed to be irrelevant to a default inference are,
in fact, irrelevant to the inference. Two formulations of default inferencing
are proposed. The first involves extending the set of defaults to include all
combinations of irrelevant properties. The second involves restricting default
inferences to deal only with relevant information. In the end, these
approaches prove to be equivalent. Properties of the resultant formal systems
are argued to correspond to common intuitions concerning defaults and
prototypical properties. Moreover the approach is argued to perhaps provide a
more appropriate basis for representing knowledge about such entities than
other existing approaches.
--
Jim Clarke -- Dept. of Computer Science, Univ. of Toronto, Canada M5S 1A4
(416) 978-4058
{allegra,cornell,decvax,linus,utzoo}!utcsri!clarke