Question

What is the purpose of an intersection entity? How do you know whether one is needed in an erd.

Answer 1

Purpose:-

• An intersection entity is used to enhance the specifications of the relationship linking the entities.
• Intersection entity is mainly used between entities having many-to-many (or N:N) relation.

Consider the following scenario:-

Here an instance of X is related to many instances of Y and vice-versa. Thus when we need to gather specifications related to a particular instance of X that is related to Y we introduce a intersection entity between X and Y.

For Example:-

• The following ERD gives a glimpse of what an intersection entity does.
• Here shipment intersects Commodity, Storehouse and Supplier that hold many-to-many relation.