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ER Diagrams 1

The overall logical structure of a database can be expressed graphically by an ER diagram . It consists of
rectangles - which represents entity sets ,
ellipses - which represents attributes,
diamonds - which represents relationship among entity sets and
lines which links attributes to entity sets, attributes to relationship sets and entity sets to relationship. Each component is labeled with the entity or relationship or attribute it represents.
To distinguish among the four types of mapping cardinalities type, we shall draw either a directed or undirected line segment between the relationship set and the entity set.


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