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Difference between Strong and Weak Entity
  • Difficulty Level : Medium
  • Last Updated : 22 Apr, 2020

Prerequisite – ER Model
Strong Entity:
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.

Weak Entity:
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.NOStrong EntityWeak 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.
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