Rules for migrating from ER and EER diagrams to Object-Relationship (OR) diagrams

Abstract

The entity relationship (ER) approach, initially proposed by [2], modified and extended by others, has been very successful as a tool for communication between the designer and the end user during the requirements analysis and conceptual design phases because of its ease of understanding and its convenience in representation. It still remains the premier model for conceptual database design. Since Chen's (1976) original ER model did not include the notion of inheritance, the ER model was later extended by others to include the notion of inheritance, and labeled the extended entity relationship (EER) model. The ER and EER models enhance the designer's ability to capture real data requirements accurately because they require one to focus on greater semantic detail in the data relationships. The ER and EER models lead to relational database design, which was widely used in the 1980's and 1990's. Relational databases, which only model the structural aspect of a database, are no longer adequate to model today's complex applications such as CAD, expert systems, flexible manufacturing systems, knowledge based systems, multimedia information systems, etc. A more powerful data model, the object-oriented data model, which captures the semantic-integrity constraints and semantic relationships that are important to many types of applications, a model that models both the structural (or static) and behavioral (or dynamic) aspects of real world objects, is needed to model such applications. Object-oriented data models, in comparison to other data models (e.g., flat relational model or nested relational models), offer richer constructs for building complex objects and provide reuse through inheritance. Object-oriented databases (OODB) are quickly becoming the state-of-the art database technology [3].