Managing Inheritance Hierarchies in Object/Relational Mapping Tools

We study, in the context of object/relational mapping tools, the problem of describing mappings between inheritance hierarchies and relational schemas. To this end, we introduce a novel mapping model, called M2ORM2+H, and investigate its mapping capabilities. We first show that M2ORM2+H subsumes three well-know basic representation strategies for mapping a hierarchy to relations. We then show that M2ORM2+H also allows expressing further mappings, e.g., where the three basic strategies are applied independently to different parts of a multi-level hierarchy. We describe the semantics of M2ORM2+H in term of how CRUD (i.e., Create, Read, Update, and Delete) operations on objects (in a hierarchy) can be translated into operations over a corresponding relational database. We also investigate correctness conditions.