T.: Querying temporal databases via OWL 2 QL

Abstract. SQL:2011, the most recently adopted version of the SQL query language, has unprecedentedly standardized the representation of temporal data in relational databases. Following the successful paradigm of ontology-based data access, we develop a practical approach to query-ing the SQL:2011-based temporal data model via the semantic layer of OWL 2 QL. The interval-based temporal query language (TQL), which we propose for this task, is based on naturally characterizable combina-tions of temporal logic with conjunctive queries. As the central contribu-tion, we present rules for sound and complete rewriting of TQL queries into two-sorted first-order logic, and consequently, into corresponding SQL queries, which can be evaluated in any existing relational database management system compliant with the SQL:2011 temporal data model. Importantly, the proposed rewriting is based on the direct reuse of the standard rewriting techniques for conjunctive queries under OWL 2 QL. This renders our approach modular and easily implementable. As a no-table corollary, we show that the data complexity of TQL query answer-ing remains in AC0, i.e., as in the usual, non-temporal case.