 - The entity-relationship model (or ER model) is a way of graphically representing the logical relationships of entities (or objects) in order to create a database. The ER model was first proposed by Peter Pin-Shan Chen of Massachusetts Institute of Technology (MIT) in the 1970s.
In ER modeling, the structure for a database is portrayed as a diagram,
called an entity-relationship diagram (or ER diagram), that resembles the graphical breakdown of a sentence
into its grammatical parts. Entities are rendered as points, polygons,
circles, or ovals. Relationships are portrayed as lines connecting the
points, polygons, circles, or ovals. Any ER diagram has an equivalent
relational table, and any relational table has an equivalent ER diagram. ER
diagramming is an invaluable aid to engineers in the design, optimization,
and debugging of database programs.
In a logical sense, entities are the equivalent of grammatical nouns,
such as employees, departments, products, or networks. An entity can be
defined by means of its properties, called attributes. Relationships are the
equivalent of verbs or associations, such as the act of purchasing, the act
of repairing, being a member of a group, or being a supervisor of a
department. A relationship can be defined according to the number of
entities associated with it, known as the degree.
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01 Apr 2005
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