  Conjunctive query (CQ) answering over knowledge bases is an important
reasoning task. However, with expressive ontology languages such as OWL, query
answering is computationally very expensive. The PAGOdA system addresses this
issue by using a tractable reasoner to compute lower and upper-bound
approximations, falling back to a fully-fledged OWL reasoner only when these
bounds don't coincide. The effectiveness of this approach critically depends on
the quality of the approximations, and in this paper we explore a technique for
computing closer approximations via RSA, an ontology language that subsumes all
the OWL 2 profiles while still maintaining tractability. We present a novel
approximation of OWL 2 ontologies into RSA, and an algorithm to compute a
closer (than PAGOdA) lower bound approximation using the RSA combined approach.
We have implemented these algorithms in a prototypical CQ answering system, and
we present a preliminary evaluation of our system that shows significant
performance improvements w.r.t. PAGOdA.
