Negative Reasoning Using Inheritance

This paper presents methods of default reasoning which allow us to draw negative conclusions that are not available in some of the models for inheritance reasoning. Some of these negative conclusions are shown to be logically required, while others result from an extension of the model to include the notion of a default negative assumption. The negative default assumption operator is exactly symmetrical to positive default assumption, and supports the drawing of extra negative conclusions. It is argued that in some domains negative conclusions are extremely important. An example is given from the medical domain to illustrate the usefulness of techniques for deducing negative facts. A formal definition of the inheritance model used, which in an earlier paper by the same author [Padgham 88] was shown to resolve a number of the classical problems in the literature on inheritance reasoning, is also given.