Titre : Ontology-based Data Access: A Study through Disjunctive Datalog, CSP, and MMSNP Exposant : Meghyn Bienvenu Résumé : Ontology-based data access is concerned with querying incomplete data sources in the presence of domain-specific knowledge provided by an ontology. A central notion is that of an ontology-mediated query, which is a database query coupled with an ontology. In this work, we study several classes of ontology-mediated queries, where the database queries are given as some form of conjunctive query and the ontologies are formulated in description logics or other relevant fragments of first-order logic, such as the guarded fragment and the unary-negation fragment. We characterize the expressive power of ontology-mediated queries in terms of fragments of disjunctive datalog and establish intimate connections between ontology-mediated queries and constraint satisfaction problems (CSPs) and their logical generalization, MMSNP formulas. By exploiting these connections, we obtain new results regarding (i) first-order rewritability and datalog-rewritability of ontology-mediated queries, (ii) P/NP dichotomies for ontology-mediated queries, and (iii) the query containment problem for ontology-mediated queries. Joint work with: Balder ten Cate, Carsten Lutz, Frank Wolter.