A Logic for Representing Default and Prototypical Properties

Abstract

The area of default reasoning may be considered as consisting of two separate but closely related subareas . The first deals with representing default information . and addresses issues such as reasoning about default statements or determining the consistency of a set of defaults . The second addresses reasoning about the default properties of an individual. given a set of default statements . Most extant .work in default reasoning has concentrated on the second area . This paper addresses the first area only. as an initial investigation into the area of default reasoning. The approach is based on adding a "variable conditional" operator to first-order logic. This operator is used to express prototypical. rather than strict . relations between ·entities and properties . A possible worlds semantics is provided for the logic along with a proof theory ; soundness and completeness results are also provided . It is argued that the variable conditional in the logic captures common intuitions concerning defaults and prototypical properties .