Extracting Ontologies from Relational Databases

The use of a conceptual model (or an ontology) to describe relational data sources has been proved to be extremely useful to overcome many important data access problems. However, the task of wrapping relational data sources by means of an ontology is mainly done manually. In this paper we introduce an automatic procedure for extracting a conceptual view from a relational database. The semantic mapping between the database schema and its conceptualisation is captured by associating views over the data source to elements of the extracted conceptual model. To represent the conceptual model we use an ontology language, rather that a graphical notation, in order to provide a precise formal semantics. In particular we adopt a variant of the DLR-Lite description logic because of its nice computational properties, and ability to express the mostly used modelling constraints. In order to uncover the connections between relational schema and the conceptual model, the heuristics underlying the ontology extraction process are based on ideas of standard relational schema design and normalisation. In fact, we assume that the relational source is in third normal form, and designed by means of a principled methodology; e.g. using EntityRelationship or UML diagrams.