Foundations of Ontology−Based Data Access under Bag Semantics

摘要: Abstract Ontology-based data access (OBDA) is a popular approach for integrating and querying multiple sources by means of shared ontology. The ontology linked to the using mappings, which assign predicates views over data. conventional semantics OBDA set-based—that is, extension defined mappings does not contain duplicate tuples. This treatment however, in disagreement with standard database management systems general, based on bags where tuples are retained default. distinction between set bag databases very significant practice, it influences evaluation aggregate queries. In this article, we propose study provides solid foundation future analytic Our compatible both set-based OBDA. Furthermore, existing bag-based exchange recently proposed literature. We show that adopting makes conjunctive query answering coNP -hard complexity. To regain tractability answering, consider suitable restrictions along three dimensions, namely, language, adoption unique name assumption. investigation shows complete picture computational properties under ontologies DL-Lite family.