Abstract
Ontology-mediated query answering is a popular
paradigm for enriching answers to user queries with
background knowledge. For querying the absence of
information, however, there exist only few ontologybased approaches. Moreover, these proposals con-
flate the closed-domain and closed-world assumption, and therefore are not suited to deal with the
anonymous objects that are common in ontological
reasoning. We propose a new closed-world semantics for answering conjunctive queries with negation
over ontologies formulated in the description logic
ELH?, based on the minimal canonical model. We
propose a rewriting strategy for dealing with negated
query atoms, which shows that query answering is
possible in polynomial time in data complexity