Abstract
To support the Semantic Web, it will be necessary to construct mappings between legacy database schemas and ontologies. We have developed a prototype tool which starts from a simple set of correspondences from table columns to ontology components, and then helps derive algorithmically candidate logical mappings between complete tables and the ontology. We report here some refinements of this algorithm inspired by an analysis of the ways in which relational schemas are standardly derived from Extended Entity Relationship diagrams, and relate this to the main heuristic used by the Clio system [6], which maps between relational database schemas.