  So-called combined approaches answer a conjunctive query over a description
logic ontology in three steps: first, they materialise certain consequences of
the ontology and the data; second, they evaluate the query over the data; and
third, they filter the result of the second phase to eliminate unsound answers.
Such approaches were developed for various members of the DL-Lite and the EL
families of languages, but none of them can handle ontologies containing
nominals. In our work, we bridge this gap and present a combined query
answering approach for ELHO---a logic that contains all features of the OWL 2
EL standard apart from transitive roles and complex role inclusions. This
extension is nontrivial because nominals require equality reasoning, which
introduces complexity into the first and the third step. Our empirical
evaluation suggests that our technique is suitable for practical application,
and so it provides a practical basis for conjunctive query answering in a large
fragment of OWL 2 EL.
