With the fast development of Semantic Web, more and more RDF and OWL ontologies are created and shared. The effective management, such as storage, inference and query, of these ontologies on databases gains increasing attentions. This paper addresses ontology query answering by means of a Datalog program, specifically tailored to bridge ontologies and databases. Introducing meta integrity constraints inspired by epistemic interpretations, we believe such a Datalog program suitable to capture ontologies in the DB favor, while keeping reasoning tractable -- Here, we present a logical equivalent knowledge base whose (sound and complete) inference system appears to a Datalog program. As such, a deductive RDF database is responsible for SPARQL query answering involved in OWL and SWRL. Bi-directional strategies, taking advantage of both forward and backward chaining, are then studied to support for this kind of customized Datalog programs, returning exactly answers to the query with respect to its logical framework.