Entity–relationship model: Difference between revisions

Revision as of 15:57, 10 June 2006

Revision as of 10:25, 11 June 2006

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[[Image:erd-entity-with-attribute.png|frame|An entity with an attribute]]

[[Image:erd-relationship-with-attribute.png|frame|A relationship with an attribute]]

[[Image:Erd-id-as-primary-key.png|frame|[[Primary key]]]]

[[Image:ER_Diagram_MMORPG.png|thumb|A sample ER diagram]]

An [[entity]] represents a discrete object. Entities can be thought of (roughly) as [[noun]]s. Examples: a computer, an employee, a song, a mathematical theorem. A [[relationship]] captures how two or more entities are related to one another. Relationships can be thought of (again, roughly) as [[verb]]s. Examples: an ''owns'' relation between a company and a computer, a ''supervises'' relation between an employee and a department, a ''performs'' relation between an artist and a song, a ''proved'' relation between a mathematician and a theorem. Entities are drawn as rectangles, relationships as diamonds.