Difference between Strong and Weak Entity
Prerequisite – ER Model
A strong entity is not dependent on 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 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. This relationship is also known as identifying relationship.
Difference between Strong and Weak Entity:
|S.NO||Strong Entity||Weak Entity|
|1.||Strong entity always has a primary key.||While a weak entity has a partial discriminator key.|
|2.||Strong entity is not dependent on any other entity.||Weak entity depends on strong entity.|
|3.||Strong entity is represented by a single rectangle.||Weak entity is represented by a double rectangle.|
|4.||Two strong entity’s relationship is represented by a single diamond.||While the relation between one strong and one weak entity is represented by a double diamond.|
|5.||Strong entities have either total participation or not.||While weak entity always has total participation.|
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