Difference between Strong and Weak Entity
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.
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. |
Last Updated :
22 Feb, 2023
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