Identifying Entity Relationships in DBMS

DBMSDatabaseMySQL

Identifying entity relationships in DBMS is used to identify a relationship between strong and weak entity.

Before beginning, let us take an example of Professor entity, which is our Strong Entity, with Professor_ID as a Primary Key 

Professor_ID
Professor_Name
Professor_City
Professor_Salary


The weak entity is Professor_Dependents entity:

Name
DOB
Relation

Now, let us continue,

Weak Entity

Weak Entity is dependent on Strong Entity and does not have a primary key. Weak Entity has a partial key. It is represented as double rectangle −

Strong Entity

Other entities are dependent on Strong Entity and it has a key attribute i.e. a primary key and represented as a single rectangle.

Identifying Relationships

It links the strong and weak entity and is represented by a double diamond sign.

Let us see with an example to link both the entities using Identifying Relationships:

Above we saw that, Dependent Name could not exist on its own but in relationship to a Professor.

Rest, the following we used in our E-R Diagram − 

Professor
Strong Entity
Dependent
Weak Entity
Partial Key (Weak Entity)
Name
Primary Key (Strong Entity)
ID
raja
Published on 03-Jul-2018 12:58:04
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