Abstract
The Ontology-Based Data Access (OBDA) systems allows users to access external databases through a conceptual domain view, given in terms of an ontology. This semantic technology addresses such problems as conceptual modeling, query rewriting, an source-to-target mapping. We show how these issues have been defined and implemented in the DAFO system, highlighting those features that distinguish it from the standard OBDA system. We propose an original approach to cope with the trade-off between expressiveness of the ontology-based conceptual modelling and ontology-mediated query rewriting in the DAFO systems. For this purpose, we divide ontological rules into three parts: (a) rewriting rules, (b) rules defining intensional predicates (views), and (c) constraint rules (satisfied in the database). This allows to balance the semantic power of the conceptual modeling and the effciency of query answering in the DAFO system, where queries are based on the faceted query paradigm.
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