These approaches create an ontology model from a relational database model and migrates the contents of the database to the generated ontology. The mappings here are simply the correspondences between each created ontological component (concept, property, etc.) and its original database component(table, column, etc.). In these approaches, the database model and the generated ontology are very similar. Mappings are quite direct and complex mapping situations do not usually appear. The creation of ontology structure may be straightforward, involving direct transformations of database tables to ontology concepts and columns into properties. This type of direct mapping is not sufficient for expressing the full semantics of the database domain. The creation of ontology structure may require the
discovery of additional semantic relations between database components (like the referential constraints) and take them into account while constructing ontology concepts and relations between them.