Enhanced entity–relationship model

The enhanced entity–relationship (EER) model (or extended entity–relationship model) in computer science is a high-level or conceptual data model incorporating extensions to the original entity–relationship (ER) model, used in the design of databases. This is the enhanced model of ER-Model It was developed to reflect more precisely the properties and constraints that are found in more complex databases, such as in engineering design and manufacturing (CAD/CAM), telecommunications, complex software systems and geographic information systems (GIS).

Mechanics

See also: Entity–relationship model and Unified Modeling Language

The EER model includes all of the concepts introduced by the ER model. Additionally it includes the concepts of a subclass and superclass (Is-a), along with the concepts of specialization and generalization. Furthermore, it introduces the concept of a union type or category, which is used to represent a collection of objects that is the union of objects of different entity types.

Subclass and superclass

Entity type Y is a subtype (subclass) of an entity type X if and only if every Y is necessarily an X. A subclass entity inherits all attributes and relationships of its superclass entity. This property is called the attribute and relationship inheritance. A subclass entity may have its own specific attributes and relationships (together with all the attributes and relationships it inherits from the superclass). Most common superclass examples is a vehicle with subclasses of Car and Truck. There are a number of common attributes between a car and a truck, which would be part of the Superclass, while the attributes specific to a car or a truck (such as max payload, truck type...) would make up two subclasses.

Tools

• The MySQL Workbench offers creating, editing and exporting EER Models. Exporting to PNG and PDF allows easy sharing for presentations.
• Skipper allows to create, import and export from ORM schema definitions to editable EER models.

See also

• Object-relational database
• Structured type

Further reading

Textbooks discussing EER and implementation using purely relational databases:

• Elmasri, Ramez; Navathe, Shamkant B. (2011). Fundamentals of Database Systems (6th ed.). Pearson/Addison Wesley. Chapters 8 and 9. ISBN 0-136-08620-9.
• Coronel, Carlos; Morris, Steven; Rob, Peter (2011). Database Systems: Design, Implementation, and Management (9th ed.). Cengage Learning. Chapter 5. ISBN 978-0-538-46968-5.
• Connolly, Thomas M.; Begg, Carolyn E. (2005). Database Systems: A Practical Approach to Design, Implementation, and Management (4th ed.). Addison-Wesley. Chapters 12 and 16. ISBN 978-0-321-21025-8.

Booklet discussing EER and implementation using object-oriented and object-relational databases:

• Dietrich, Suzanne W.; Urban, Susan D. (2011). Fundamentals of Object Databases: Object-Oriented and Object-Relational Design. Morgan & Claypool Publishers. ISBN 978-1-60845-476-1.

Textbook discussing implementation in relational and object-relational databases:

• Ricardo, Catherine (2011). Databases Illuminated (2nd ed.). Jones & Bartlett Publishers. Chapter 8. ISBN 978-1-4496-0600-8.

Shorter survey articles:

• Teorey, Toby J.; Yang, Dongqing; Fry, James P. (1986). "A logical design methodology for relational databases using the extended entity–relationship model". ACM Computing Surveys. 18 (2): 197–222. CiteSeerX 10.1.1.105.7211. doi:10.1145/7474.7475.
• Sikha Bagui (2006). "Extended Entity Relationship Modeling". In Laura C. Rivero; Jorge H. Doorn; Viviana E. Ferraggine (eds.). Encyclopedia of Database Technologies and Applications. Idea Group Inc (IGI). pp. 233–239. ISBN 978-1-59140-795-9.

External links

• [1] - Slides for chapter 8 from Fundamentals of Database Systems by Elmasri and Navathe (Pearson, 2011)
• [2] - Lecture notes from the University of Toronto
• [3] - The ER Conference