Relationship

• A relationship is used to describe the relation between entities.

• Diamond or rhombus is used to represent the relationship.

Types of relationship:

There are four types of relationship:

1. One-to-One Relationship

2. One-to-Many Relationship

3. Many-to-One Relationship

4. Many-to-Many Relationship

One-to-One Relationship

When only one instance of an entity is associated with the relationship, then it is known as one to one relationship.

One-to-many relationship

When only one instance of the entity on the left, and more than one instance of an entity on the right associates with the relationship then this is known asaone-to- many relationship.

Many-to-one relationship

When more than one instance of the entity on the left, and only one instance of an entity on the right associates with the relationship then it is known asamany-to- one relationship.

Many-to-many relationship

When more than one instance of the entity on the left, and more than one instance of an entity on the right associates with the relationship then it is known asamany-to- many relationship.