John F. Horty

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Early attempts at combining multiple inheritance with nonmonotonic reasoning were based on straight forward extensions of tree-structured inheritance systems, and were theoretically unsound. In The Mathematics of Inheritance Systems, or TMOIS, Touretzky described two problems these systems cannot handle: reasoning in the presence of true but redundant(More)
This paper describes a new approach to inheritance reasoning in semantic networks allowing for multiple inheritance with exceptions. The approach leads to an analysis of defeasible inheritance which is both well-defined and intuitively attractive: it yields unambiguous results applied to any acyclic semantic network, and the results conform to our(More)
  • John F. Horty
  • Annals of Mathematics and Artificial Intelligence
  • 1993
Ever since its inception in the work of von Wright, deontic logic has been developed primarily as a species of modal logic. I argue in this paper, however, that the techniques of nonmonotonic logic may provide a better theoretical framework — at least for the formalization of commensense normative reasoning — than the usual modal treatment. After reviewing(More)
Much of the recent literature on reasons is focused on a common range of issues, concerning, for example, the relation between reasons and motivation, desires, and values, the issue of internalism versus externalism in the theory of reasons, or the objectivity or reasons. This paper is concerned with a different, and orthogonal, set of questions: What are(More)
The view update problem is considered in the context of deductive databases where the update of an intensional predicate is accomplished by modifying appropriately the underlying relations in the extensional database. Two classes of disjunctive databases are considered. The first class contains those disjunctive databases which allow only definite rules in(More)
Subtle differences in the method of constructing arguments in inheritance systems can result in profound differences in both the conclusions reached and the efficiency of inference. This paper focuses on issues surrounding the defeat of arguments in nonmonotonic inheritance. Looking primarily at skeptical reasoners, we analyze several types of defeat that(More)