Reference: Fikes, R.; Hayes, P.; & Horrocks, I. OWL-QL - A Language for Deductive Query Answering on the Semantic Web. Knowledge Systems Laboratory, Stanford University, Stanford, CA, 2003.
Abstract: This paper discusses the issues involved in designing a query language for the Semantic Web and presents the OWL Query Language (OWL-QL) as a candidate standard language and protocol for query-answering dialogues among Semantic Web computational agents using knowledge represented in the W3C's Ontology Web Language (OWL). OWL-QL is a formal language and precisely specifies the semantic relationships among a query, a query answer, and the knowledge base(s) used to produce the answer. Unlike standard database and Web query languages, OWL-QL supports query-answering dialogues in which the answering agent may use automated reasoning methods to derive answers to queries, as well as dialogues in which the knowledge to be used in answering a query may be in multiple knowledge bases on the Semantic Web, and/or where those knowledge bases are not specified by the querying agent. In this setting, the set of answers to a query may be of unpredictable size and may require an unpredictable amount of time to compute.
Full paper available as doc, pdf.