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Difference Between Strong and Weak Entity - Testbook.com

Last Updated on Jul 31, 2023

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In the realm of data management and databases, entities are unique objects that possess a set of attributes. These entities can be divided into two categories - strong entities and weak entities. The primary difference lies in their dependency: strong entities function independently, while weak entities rely on other entities. Let's delve deeper into the distinctive features of strong and weak entities.

Exploring the Concept of a Strong Entity
A strong entity is a standalone entity that does not require support from any other entity. It's marked by the presence of a primary key, which signifies its distinct identity in a table.

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Unraveling the Nature of a Weak Entity
Contrary to a strong entity, a weak entity is dependent and cannot exist independently. It requires the support of a strong entity to validate its existence.

Comparing Strong and Weak Entities

S.No. Strong Entity Weak Entity

1 Operates independently. Requires support from a strong entity.

2 Possesses a primary key. Lacks a primary key.

3 Represented by a single rectangle in diagrams. Denoted by a double rectangle in diagrams.

4 The relationship between two strong entities is denoted by a single diamond. The relationship between a weak and a strong entity is denoted by a double diamond.

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Frequently Asked Questions

What is a Strong Entity?

A strong entity is an entity that is not dependent on any other entity. It has a primary key, or a table includes a primary key.

What is a Weak Entity?

Unlike a strong entity, a weak entity is not independent as it is reliant on another strong entity. It has to rely on other entities to ensure its existence.

What are the main differences between a strong and a weak entity?

A strong entity is independent, has a primary key and is depicted by a sole rectangle. In contrast, a weak entity is dependent on a strong entity, does not have a primary key and is depicted by a dual rectangle.

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S.No.	Strong Entity	Weak Entity
1	Operates independently.	Requires support from a strong entity.
2	Possesses a primary key.	Lacks a primary key.
3	Represented by a single rectangle in diagrams.	Denoted by a double rectangle in diagrams.
4	The relationship between two strong entities is denoted by a single diamond.	The relationship between a weak and a strong entity is denoted by a double diamond.