Schema transformations and query rewriting in ontological databases with a faceted interface

Abstract

In this paper, we discuss some problems identified in designing and implementing a class of ontological database systems. The goal of these systems is to provide an extended knowledge system that combines flexibility of ontologies with efficiency of relational databases. The terminological part of the ontology forms the ontological (conceptual) schema of the database, and the extensional part is managed by a relational database server. Queries are formulated in an interactive way using a faceted search over the ontological schema. In such scenario, a number of transformations must be performed: (a) a mapping from an ontological schema into relational scheme that concerns both the structure and rules constituting the ontology; (b) transformation of faceted queries, defined in a graphical form, into first-order queries and to SQL queries. The considerations are based on verified solutions implemented in DAFO (Data Access based in Faceted queries over Ontologies) system.