Strong entity และ weak entity ม ความแตกต างก นอย างไร

Prerequisite – ER Model 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.

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:

S.NO Strong Entity Weak Entity 1. Strong entity always has a primary key. While a weak entity has a partial discriminator key. 2. Strong entity is not dependent on any other entity. Weak entity depends on strong entity. 3. Strong entity is represented by a single rectangle. Weak entity is represented by a double rectangle. 4. 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. 5. Strong entities have either total participation or not. While weak entity always has total participation.

Last Updated : 22 Feb, 2023

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The main difference between weak entity and strong entity is that weak entity depends on a strong entity while a strong entity is an entity that does not depend on another entity.

help to visually represent databases. In ER modeling, we can create entities, attributes, and in order to understand how data is related to each other. Moreover, entity is an important concept used in ER diagrams. It is a real-world object that represents data. More importantly, attributes are the characteristics of an entity. There are two types of entities called strong entity and weak entity. In brief, weak entity always depends on a strong entity.

Key Areas Covered

1. – Definition, Functionality 2. – Definition, Functionality 3. – Comparison of Key Differences

Key Terms

Entity, ER Diagrams, Strong Entity, Weak Entity

A weak entity is an entity that depends on a strong entity. For example, in a university database, there are entities called course and exam. The exam is based on the course. Exam name, questions, etc. depend on the course. Therefore, the course entity is a strong entity because it does not rely on some other entity. On the other hand, exam is a weak entity as it relies on the strong entity.

A weak entity does not have a primary key. It has a composite key, which is a of a strong entity and a partial key of the weak entity. A set of weak entities create a weak entity set. In an ER diagram, a double rectangle represents a weak entity. Furthermore, the relationship between a strong entity and a weak entity is a denoted by a double diamond.

What is a Strong Entity

A strong entity is an entity that does not depend on another entity. For instance, assume a university management system. It stores details about students and lecturers. There are separate tables to enter student records and lecturer records. Student and lecturer are entities in the ER diagram. Similarly, a medical center management system store details about patients, doctors, etc. Patients and doctors are separate tables in the database. Thus, these are strong entities.

A strong entity has a primary key. Therefore, we can identify each entity in a strong entity set. A set of strong entities create a strong entity set. In ER diagrams, a rectangle is used to denote a strong entity. Furthermore, a single diamond represents the relationship between two strong entities.

Difference Between Weak Entity and Strong Entity

Definition

A weak entity is an entity that cannot be uniquely identified by its attributes alone whereas a strong entity is an entity that is independent of any other entity in a schema. Thus, this is the main difference between weak entity and strong entity.

Dependency

Importantly, a weak entity always depends on a strong entity, but a strong entity does not depend on another entity.

ER Diagram Representation

Another difference between weak entity and strong entity is that a double rectangle denotes a weak entity while a rectangle represents a strong entity.

Key Attributes

Moreover, a weak entity does not have any key attribute on its own while a strong entity has a key attribute. Hene, this is an important difference between weak entity and strong entity.

Conclusion

In brief, an entity is a real-world object that represents data. Moreover, there are two types of entities as weak entity and strong entity. The main difference between weak entity and strong entity is that weak entity depends on a strong entity while a strong entity is an entity that does not depend on another entity.

Reference:

1. “Working with ER Diagrams.” Studytonight, Available here. 2. “Weak Entity.” Wikipedia, Wikimedia Foundation, 3 Apr. 2019, Available here.

Image Courtesy:

1. “Weak entity ER-example” By Mixer – Using Dia software especially for Wikipedia’s “Weak entity” article (CC BY-SA 3.0) via Commons Wikimedia

About the Author: Hasa

Hasanthi is a seasoned content writer and editor with over 8 years of experience. Armed with a BA degree in English and a knack for digital marketing, she explores her passions for literature, history, culture, and food through her engaging and informative writing.

What is the relationship between a strong and a weak entity?

The relation between one strong and one weak entity is represented by a double diamond. This relationship is also known as identifying relationship. 1. Strong entity always has a primary key. While a weak entity has a partial discriminator key. 2. Strong entity is not dependent on any other entity. Weak entity depends on strong entity. 3.

How many types of entities are there?

There are two types entities namely strong entity and weak entity. A strong entity is an independent entity. On the other hand, a weak entity is a dependent entity that depends on a strong entity. Read through this article to find out more about strong and weak entities and how they are different from each other. What is a Strong Entity?

How the composed primary key of a weak entity identify each entity?

This is how the composed primary key of weak entity identify each entity in weak entity set. The basic difference between strong entity and a weak entity is that the strong entity has a primary key whereas, a weak entity has the partial key which acts as a discriminator between the entities of a weak entity set.

What is a strong entity set?

It indicates that each entity in a strong entity set can be uniquely identified. Set of similar types of strong entities together forms the Strong Entity Set. A strong entity holds the relationship with the weak entity via an Identifying Relationship, which is denoted by double diamond in the ER diagram.