Identifying Entity Relationships in DBMS

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 −

The weak entity is Professor_Dependents entity:

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 −