[6]. The conceptual level matching mechanism of semantic information retrieval can make machine fully understand user's retrieval requests. In general, ontology is described by certain description logic based language, such as RDF(S), SHOE and OWL etc. Some commonly-used ontology tools such as Protégé, Jena and what not can execute automatic reasoning to meet the needs of intelligent information retrieval.
Solely relying on precise ontology cannot express all semantics about words in limited expression, that is, knowledge in precise ontology is incomplete, so rough ontology is introduced. Rough ontology is an extension to precise ontology with rough set theory