  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 ontology-based approaches. Moreover,
these proposals conflate the closed-domain and closed-world assumption, and
therefore are not suited to deal with the anonymous objects that are common in
ontological reasoning. Many real-world applications, like processing electronic
health records (EHRs), also contain a temporal dimension, and require efficient
reasoning algorithms. Moreover, since medical data is not recorded on a regular
basis, reasoners must deal with sparse data with potentially large temporal
gaps. Our contribution consists of two main parts: In the first part we
introduce a new closed-world semantics for answering conjunctive queries with
negation over ontologies formulated in the description logic ELHb, which is
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. In the second part, we extend this
minimal-world semantics for answering metric temporal conjunctive queries with
negation over the lightweight temporal logic TELHb and obtain similar
rewritability and complexity results. This paper is under consideration in
Theory and Practice of Logic Programming (TPLP).
