A Tutorial on Default Logics

A Tutorial on Default LogicsGRIGORIS ANTONIOUGriffith UniversityDefault Logic is one of the most prominent approaches to nonmonotonic reasoning,and allows one to make plausible conjectures when faced with incompleteinformation about the problem at hand. Default rules prevail in many applicationdomains such as medical diagnosis and legal reasoning.Several variants have been developed over the past years, either to overcome someperceived deficiencies of the original presentation, or to realize somewhat differentintuitions. This paper provides a tutorial-style introduction to some importantapproaches of Default Logic. The presentation is based on operational models forthese approaches, thus making them more easily accessible to a broader audience,and more easily usable in practical applications.Categories and Subject Descriptors: I.2.3 [Artificial Intelligence]: Deduction andTheorem Proving—Nonmonotonic reasoning and belief revision; I.2.4 [ArtificialIntelligence]: Knowledge Representation Formalisms andMethods—Representation languagesGeneral Terms: Languages, TheoryAdditional Key Words and Phrases: Default Logic, nonmonotonic reasoning,operational models1. INTRODUCTION: DEFAULT REASONING data. Classical logic indeed has the ca-pacity to represent and reason with cer-When an intelligent system (either com-tain aspects of incomplete information.puter-based or human) tries to solve aBut there are occasions where addi-problem, it may be able to rely ...