Prerequisite – ER Model
Strong entity is not dependent of any other entity in schema. Strong entity always has primary key. Strong entity is represented by single rectangle. Two strong entity’s relationship is represented by single diamond.
Various strong entities together makes the strong entity set.
Weak entity is depend on strong entity to ensure the existance of weak entity. Like strong entity weak entity does not have any primary key, It has partial discriminator key. Weak entity is represented by double rectangle.
The relation between one strong and one weak entity is represented by double diamond.
Difference between Strong and Weak Entity:
|S.NO||Strong Entity||Weak Entity|
|1.||Strong entity always has primary key.||While weak entity has partial discriminator key.|
|2.||Strong entity is not dependent of any other entity.||Weak entity is depend on strong entity.|
|3.||Strong entity is represented by single rectangle.||Weak entity is represented by double rectangle.|
|4.||Two strong entity’s relationship is represented by single diamond.||While the relation between one strong and one weak entity is represented by double diamond.|
|5.||Strong entity have either total participation or not.||While weak entity always has total participation.|
- Weak Entity Set in ER diagrams
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