Difference between Strong and Weak Entity

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.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.

Attention reader! Don’t stop learning now. Get hold of all the important CS Theory concepts for SDE interviews with the CS Theory Course at a student-friendly price and become industry ready.

My Personal Notes arrow_drop_up

Check out this Author's contributed articles.

If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.



Improved By : jlw55080

Article Tags :
Practice Tags :


2


Please write to us at contribute@geeksforgeeks.org to report any issue with the above content.