Abstract. Answering a query over a group of RDF data pages is a trivial process. However, in the Semantic Web, there is a need for ontology technology. Consequently, OWL, a family of web ontology languages based on description logic, has been proposed for the Semantic Web. Answering a query over the SemanticWeb is thus not trivial, but a deductive process. However, the reasoning on OWL with data has an efficiency problem. Thus, we introduce optimization techniques for the inference algorithm. This work demonstrates the techniques for instance checking and instance retrieval problems with respect to ALC description logic which covers certain parts of OWL. 1 Motivation The Semantic Web, originated from an idea of the creator of the Web Tim Berners-lee [3], is an effort to bring back structure to information available on the Web. The structures are semantic annotations that conform to an explicit specification (called ontology) of the intended meaning of a piece of information. Thus the...