Querying the Semantic Web: A Formal Approach

Ontologies are set to play a key role in the Semantic Web, and several web ontology languages, like DAML+OIL, are based on DLs. These not only provide a clear semantics to the ontology languages, but allows them to exploit DL systems in order to provide correct and complete reasoning services. Recent results shown that DL systems can be enriched by a conjunctive query language, providing a solution to one of the weakness of traditional DL systems. These results can be transfered to the Semantic Web community, where the need for expressive query languages is witnessed by different proposals (like DQL for DAML+OIL). In this paper we present a logical framework for conjunctive query answering in DAML+OIL. Moreover, we provide a sound and complete algorithm based on recent Description Logic research.