Explain difference between Strong Entity and Weak Entity

AlgorithmsGeneral KnowledgeProgramming

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.KeyStrong EntityWeak Entity
1KeyStrong entity always have one primary key.Weak entity have a foreign key referencing primary key of strong entity.
2DependencyStrong entity is independent of other entities.Weak entity is dependent on strong entity.
3Represented byA strong entity is represented by single rectangle.A weak entity is represented by double rectangle.
4Relationship RepresentationRelationship between two strong entities is represented by single diamond.Relationship between a strong and weak entity is represented by double diamond.
5ParticipationStrong entity may or may not participate in entity relationships.Weak entity always participates in entity relationships.
raja
Published on 15-Apr-2020 10:45:34
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