The Entity Relationship Diagram.

Essay by kalexanderUniversity, Master'sA+, December 2003

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The Entity Relationship Diagram (ERD) depicts a conceptual data model that incorporates some of the important scientific information about the real world. It adopts a natural view that the real world consists of entities and relations (Chen, 1976). One objective of the ERD is to create a simple, easy to understand and conveniently presented data model consisting of entities, attributes, relationships and cardinalities. The model serves as tool for database design, where the model can facilitate communication between the system analyst or designer and the end-user during the requirement analysis and conceptual design phases.

Chen published one of the first articles on the entity-relationship model in 1976 at a database conference (Chen, 1976). The concept of entity-relationship already existed for years in the field of philosophy and began to be applied to database design heavily between 1975 and 1980. In 1979, there was a conference on the entity-relationship model during the First International Conference on Entity-Relationship Approach in Los Angeles, California.

Annual conferences on the topic continued until 1995, when the conference was renamed the International Conference on Conceptual Modeling (AICCM, 2003). The entity-relationship model is the result of the unification of the hierarchical, network and relational models for developing a logical database design. One important purpose of the entity-relationship model was to have a database model that was independent of the existing database management systems.

An entity is defined as a person, place or thing in the real world or is conceptual, only existing in someone's mind. An entity that is specific is similar to an object instantiation of a class. Entity types are a more powerful and concise representation of entities. An entity type is a collection of entities that share a common definition. For example, an entity may be a Ford car, whereas an entity type could...