About Entities, Complex Objects and Object-oriented Data Models

Facilities for complex object modeling are nowadays needed in several areas of database applications (CAD/CAM, office automation, robotics, ...). Consequently, either new models are developed, or existing ones (relational, functional) are extended to better respond to this requirement. This paper intends to show that the entity-relationship approach may offer the required facilities, preserving the well known advantages inherent to this approach : increased readability and graphical display of the database schema. To this aim, an enhanced entity-relationship model, called ERC+ (for Entity Relationship Complex plus generalization), is presented. The associated query facilities are presented as well, in the form of an ERC+ algebra. Finally, the paper discusses how ERC+ peculiar features (complex attribute structures, multivalued attributes, duplicates) and its algebra succeed in supporting complex object management. A comparison with object-oriented models is proposed.