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 |