DBOWL is a scalable reasoner for OWL ontologies with very large Aboxes (billions of instances). DBOWL supports most of the fragment of OWL covering OWL-DL. DBOWL stores ontologies and classifies instances using relational database technology and combines relational algebra expressions and fixed-point iterations for computing the closure of the ontology, called knowledge base creation. In this paper we describe and evaluate DBOWL. For the evaluation both the standard datasets provided in the context of the ORE 2012 workshop and the