We introduce the database fragment of RDF, which extends the popular Description Logic fragment, in particular with support for incomplete information. We then provide novel sound and complete saturation- and reformulation-based techniques for answering the Basic Graph Pattern queries of SPARQL in this fragment. Notably, we extend the state of the art on pushing RDF query processing within robust / efficient relational database management systems. Finally, we experimentally compare our query answering techniques using well-established datasets.