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 MORM+HIE , and investigate its mapping capabilities. We first show that MORM+HIE subsumes three well-know basic representation strategies for mapping a hierarchy to relations. We then show that MORM+HIE 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 MORM+HIE 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.