Case study in mapping conceptual designs to object-relational schemas

The recent emergence of object-relational technology into the commercial database market has caused new challenges for the implementation of conceptual database designs. This paper presents our experience with using the Oracle 8 object-relational data model in the implementation of an engineering application described using the EXPRESS conceptual modeling language. EXPRESS is part of the engineering community's Standard for the Exchange of Product Data and can be characterized as a structurally object-oriented modeling language, supporting the notion of entities, entity hierarchies, complex constraints on entity hierarchies, relationships and inverse relationships between entities, and user-defined types. As a result, EXPRESS provides an excellent framework for studying the mapping of conceptual modeling concepts into an object-relational model. In this paper, we describe the way in which the features of EXPRESS can be mapped into object-relational features such as object tables, object references, and nested tables. We also describe the manner in which features such as member functions on object types, triggers, and stored procedures can be used to support the implementation of constraints associated with a conceptual schema. Although the mappings presented are specific to EXPRESS and Oracle 8, the mappings are generalizable to conceptual modeling languages and object-relational models with similar features. Our work defines how traditional mapping concepts must be revised in order to make adequate use of the features now found in object-relational models. As part of this paper, we also compare our mapping approach using Oracle 8 to mapping issues for the PostgreSQL object-relational model and the Objectivity/DB object-oriented data model.