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Difference between Strong and Weak Entity

  • Difficulty Level : Medium
  • Last Updated : 25 Oct, 2021

Prerequisite – ER Model 
Strong Entity: 
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. 

Weak Entity: 
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.

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Difference between Strong and Weak Entity: 
 

S.NOStrong EntityWeak 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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