• defining an entity (relation) is arbitrary (W. Kent, Data and Reality, North Holland Publishing, 1978);
• partitioning an entity into a hierarchy (Codd's normalization) is arbitrary, and there is no a priori best hierarchy for this partitioning (W.S. Jevons, The Principles of Science, Dover Publications, 1874); and
• partitioning a set of sets (concept domain) into nonoverlapping subsets is an NP-complete problem and has no polynomial time-limited algorithmic solution. The best that can be done is to test a given partitioning to see whether it has overlapping subsets. If you do not require nonoverlapping subsets, then any arbitrary partitioning will do, but you will not be able to use it for reasoning about the domain.
• J. Davies, D. Fensel, and F. van Harmelen, Towards the Semantic Web: Ontology-Driven Knowledge Management, John Wiley and Sons, 2003.
• M. Daconta, L. Obrst, and K. Smith, The Semantic Web: A Guide to the Future of XML, Web Services, and Knowledge Management, John Wiley and Sons, 2003.