Answering Counting Queries over DL-Lite Ontologies
This work addresses a gap in expressive query answering for data access and integration, but it is incremental as it builds on existing intractability results.
The paper tackles the problem of answering counting queries over DL-Lite ontologies, which are largely unexplored in ontology-mediated query answering, and establishes improved complexity bounds for practically relevant restrictions.
Ontology-mediated query answering (OMQA) is a promising approach to data access and integration that has been actively studied in the knowledge representation and database communities for more than a decade. The vast majority of work on OMQA focuses on conjunctive queries, whereas more expressive queries that feature counting or other forms of aggregation remain largely unex-plored. In this paper, we introduce a general form of counting query, relate it to previous proposals, and study the complexity of answering such queries in the presence of DL-Lite ontologies. As it follows from existing work that query answering is intractable and often of high complexity, we consider some practically relevant restrictions, for which we establish improved complexity bounds.