  Querying large datasets with incomplete and vague data is still a challenge.
Ontology-based query answering extends standard database query answering by
background knowledge from an ontology to augment incomplete data. We focus on
ontologies written in rough description logics (DLs), which allow to represent
vague knowledge by partitioning the domain of discourse into classes of
indiscernible elements.
  In this paper, we extend the combined approach for ontology-based query
answering to a variant of the DL EL augmented with rough concept constructors.
We show that this extension preserves the good computational properties of
classical EL and can be implemented by standard database systems.
