Ontology-based evaluation of fuzzy bipolar conjunctive queries over relational databases

In the wake of flexible querying system, proposed in [26], [28], [29], in which the bipolarity of the form “and if possible” is used as means to express user preferences over relational databases and ontologies (fuzzy bipolar DLR-Lite), we introduce in this paper the user query evaluation process, under the extension of our flexible querying framework to bipolar conditions of the form “or else” [20], [19]. Queries addressed to our system are bipolar conjunctive queries made of a conjunction of atoms corresponding to concepts of an ontology. The proposed evaluation process is carried out in two main steps. The former consists of query derivation to compute complementary queries, based on substitutions of query's atoms involved in fuzzy bipolar subsumptions expressed in the considered bipolar ontology. The latter deals with the translation of the obtained set of queries from the first step into bipolar SQLf statements, which are finally evaluated over a bipolar relational database managed by PostgreSQLf DBMS extended to bipolar datatypes and functions. Three algorithms are then developed in order to perform applicable substitutions, to derive corresponding complementary queries and to translate them into Bipolar SQLf statements. The feasibility of the approach is shown through a prototype developed in the field of multimodal transport systems.