Abstract
Traditionally, the AI community assumes that a knowledge base must be consistent. Despite that, there are many applications where, due to the existence of rules with exceptions, inconsistent knowledge must be considered. One way of restoring consistency is to withdraw conflicting rules; however, this will destroy part of the knowledge. Indeed, a better alternative would be to give precedence to exceptions. This paper proposes a dialogue system for coherent reasoning with inconsistent knowledge, which resolves conflicts by using precedence relations of three kinds: explicit precedence relation, which is synthesized from precedence rules; implicit precedence relation, which is synthesized from defeasible rules; mixed precedence relation, which is synthesized by combining explicit and implicit precedence relations.
Highlights
A knowledge base is a set of rules representing the knowledge of an expert in a specific domain
This paper proposes a system for coherent reasoning, based on dialogical argumentation and defeasible reasoning, which resolves conflicts by using precedence relations of three kinds: explicit precedence relation, which is synthesized from precedence rules; implicit precedence relation, which is synthesized from defeasible rules; mixed precedence relation, which is synthesized by combining explicit and implicit precedence relations
The paper is organized as follows: Section 2 introduces the fundamentals of defeasible reasoning and explains how the three kinds of precedence relations are synthesized in our system; Section 3 describes the dialectical proof procedure on which our system is based; Section 4 presents some features of the dialogue system prototype implemented in Prolog; Section 5 presents the conclusion of the paper
Summary
A knowledge base is a set of rules representing the knowledge of an expert in a specific domain. The Artificial Intelligence (AI) community assumes that a knowledge base must be free of inconsistency; otherwise, it turns out to be useless for an automated reasoning system This assumption is motivated by the ex falso quodlibet principle [1], which establishes that “from a falsehood, anything follows”. Both “Tweety flies” and “Tweety does not fly” can be inferred from ∆′ , and that is not a coherent reasoning. A better alternative would be to give precedence to the exception “penguins do not fly” In this case, only “Tweety does not fly” can be coherently inferred from ∆′. The paper is organized as follows: Section 2 introduces the fundamentals of defeasible reasoning and explains how the three kinds of precedence relations are synthesized in our system; Section 3 describes the dialectical proof procedure on which our system is based; Section 4 presents some features of the dialogue system prototype implemented in Prolog; Section 5 presents the conclusion of the paper
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