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Difference between Strong and Weak Entity

Last Updated : 15 May, 2024
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Prerequisite – ER Model 

An entity is a “thing” or “object” in the real world. An entity contains attributes, which describe that entity. So anything about which we store information is called an entity. Entities are recorded in the database and must be distinguishable, i.e., easily recognized from the group. In this article we will see difference between strong and weak entity.

What is 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.

What is 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

Strong Entity Weak Entity
Strong entity always has a primary key. While a weak entity has a partial discriminator key.
Strong entity is not dependent on any other entity. Weak entity depends on strong entity.
Strong entity is represented by a single rectangle. Weak entity is represented by a double rectangle.
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.
Strong entities have either total participation or not. weak entity always has total participation.

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