Types of Relationships

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Entity Relationship can categories into two types that Identifying Relationship and Non-Identifying Relationship.

Identify Relationship

An instance of a Child Entity is identified through its association with the Parent Entity is called Identifying Relationship and one instance of the Parent Entity is related with one or more instances of Child Entity. This kind of Child Entity is called Weak Entity.

For example, Employee and Skill are Parent Entities that related with Emp_Skill Child Entity. Employee Entity Primary Key is combined with Skill Entity Primary Key that Composite Primary Key is defined in the Emp_Skill Entity. An instance of Emp_Skill cannot identify from Emp_Skill that can identify through its associated Employee and Skill Entities.



Non-Identify Relationship

An instance of a Child Entity is identified by itself and the Child Entity is not identified through its association with the Parent Entity is called Non-Identifying Relationship and one instance of the Parent Entity is related with one or more instances of Child Entity.

For example, Department is a Parent Entity and Employee is a Child Entity. The Department Entity is designed with Dept_Code and that is Primary Key of the Department Entity. Employee Entity is designed with Dept_Code and that is Foreign Key of the Employee Entity. These entities are associated by common Dept_Code attribute between Department and Employee Entities.

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