Subtyping Revisited

In information systems modeling, the business domain being modeled often exhibits subtyping aspects that can prove challenging to implement in either relational databases or object-oriented code. In practice, some of these aspects are often handled incorrectly. This paper examines a number of subtyping issues that require special attention (e.g. derivation options, subtype rigidity, subtype migration), and discusses how to model them conceptually. Because of its richer semantics, the main graphic notation used is that of Object-Role Modeling (ORM). However, the main ideas could be adapted for UML and ER, so these are also included in the discussion. A basic implementation of the proposed approach has been prototyped in an open-source ORM tool.