Explain difference between Strong Entity and Weak Entity

Algorithms General Knowledge Programming

Strong Entity

Strong Entity is independent to any other entity in the schema. A strong entity always have a primary key. In ER diagram, a strong entity is represented by rectangle. Relationship between two strong entities is represented by a diamond. A set of strong entities is known as strong entity set.

Weak Entity

Weak entity is dependent on strong entity and cannot exists without a corresponding strong. It has a foreign key which relates it to a strong entity. A weak entity is represented by double rectangle. Relationship between a strong entity and a weak entity is represented by double diamond. The foreign key is also called a partial discriminator key.

Following are some of the important differences between Strong Entity and Weak Entity.

Sr. No.	Key	Strong Entity	Weak Entity
1	Key	Strong entity always have one primary key.	Weak entity have a foreign key referencing primary key of strong entity.
2	Dependency	Strong entity is independent of other entities.	Weak entity is dependent on strong entity.
3	Represented by	A strong entity is represented by single rectangle.	A weak entity is represented by double rectangle.
4	Relationship Representation	Relationship between two strong entities is represented by single diamond.	Relationship between a strong and weak entity is represented by double diamond.
5	Participation	Strong entity may or may not participate in entity relationships.	Weak entity always participates in entity relationships.

Mahesh Parahar

Updated on: 16-May-2020

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