The Completeness of Reasoning Algorithms for Clause Sets in Description Logic ALC

Abstract

On the Semantic Web, metadata and ontologies are used to enable computers to read data. The Web Ontology Language (OWL) has been proposed as a standard ontological language, and various inference systems for this language have been studied. Description logics are regarded as the theoretical foundations of OWL; they provide the syntax and semantics of a formal language for describing ontologies and knowledge bases. In addition, tableau algorithms for description logics have been developed as the standard reasoning algorithms for decidable problems. However, tableau algorithms generate inefficient reasoning steps owing to their nondeterministic branching for disjunction as well as the increase in the size of models occasioned by existential quantification. In this study, we propose conjunctive normal form (CNF) concepts, which utilize a flat concept form for description logic ALC in order to develop algorithms for reasoning about sets of clauses. We present an efficient reasoning algorithm for clause sets where any ALC concept is transformed into an equivalent CNF concept. Theoretically, we prove the soundness, completeness, and termination of the reasoning algorithms for the satisfiability of CNF concepts.