Solving Query-Answering Problems for the Semantic Web Using Equivalent Transformation

Abstract

Abstract-A query-answering problem (QA problem) is an "all-answers finding" problem concerning with finding all ground instances of a query atomic formula that are logical consequences of a given logical formula. Based on the equivalent transformation (ET) principle, we propose a general framework for solving QA problems on Description Logics, which are logical formalisms underlying the Ontology Web Language OWL-DL. To solve such a QA problem using this framework, axioms and assertions representing the background knowledge of the problem are converted into a conjunction of first-order formulas, which is further converted by meaning-preserving Skolemization into a set of extended clauses typically containing global existential quantifications of function variables. The obtained clause set is then transformed successively using ET rules until the answer set of the original problem can be readily derived. ET rules for unfolding extended clauses, for removing useless extended clauses, and for dealing with function variables are presented. Application of the framework is illustrated.