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Entity Relationship Diagram Notation

 

Entity

 

The name of an entity is written in its own compartment.

 

 

 

Entity Attribute Compartment

 

If an entity has attributes they are displayed in an entity attribute compartment placed below the name compartment. Each attribute is given preceded by its type.

 

 

 

One Unconditional Relationship    -->

 

 

 

One Conditional Relationship    -|>

 

 

 

Many Unconditional Relationship    ->>

 

 

 

Many Conditional Relationship    |>>

 

 

 

Entity Identifier Compartment

 

If one or more identifiers are defined for an entity they are displayed in a entity identifier component. An identifier is named and an indented list of attributes which make the identifier is given. If the identifier includes attributes from other entities these must be specified as identifiers of those other entities.

 

 

 

Identifier Example

 

The Dog Owner entity has an identifier which is formed from a single attribute called name. The Dog entity has an identifier that is made up from the Dog's attribute called name plus the Dog Owner's name contained within Dog Owner Identifier. To be able to identify a particular dog the dog's owner name and the dog's name must be supplied. The relationship must be single unconditional as shown.

 

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