Prerequisite – ER Model
A strong entity is not dependent of any other entity in the schema. A strong entity will always have a primary key. Strong entities are represented by a single rectangle. The relationship of two strong entities is represented by a single diamond.
Various strong entities, when combined together, create a strong entity set.
A weak entity is dependent on a strong entity to ensure the its existence. Unlike a strong entity, a weak entity does not have any primary key. It instead has a partial discriminator key. A weak entity is represented by a double rectangle.
The relation between one strong and one weak entity is represented by a 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.|