Absorption-Based Query Answering for Expressive Description Logics

Abstract

Conjunctive query answering is an important reasoning task for logic-based knowledge representation formalisms, such as Description Logics, to query for instance data that is related in certain ways. Although many knowledge bases use language features of more expressive Description Logics, there are hardly any systems that support full conjunctive query answering for these logics. In fact, existing systems usually impose restrictions on the queries or only compute incomplete results. In this paper, we present a new approach for answering conjunctive queries that can directly be integrated into existing reasoning systems for expressive Description Logics. The approach reminds of absorption, a well-known preprocessing step that rewrites axioms such that they can be handled more efficiently. In this sense, we rewrite the query such that entailment can dynamically be checked in the dominantly used tableau calculi with minor extensions. Our implementation in the reasoning system Konclude outperforms existing systems even for queries that are restricted to the capabilities of these other systems.