Relationship

Relational databases have various relationships that can be depicted on diagrams.

There are different dependencies between entities, and each defines the interaction between a number of elements. An element can interact with several or only one, which is referred to as a relationship.

Relational databases have various relationships that can be depicted on diagrams.

Types of relationships:

• One-to-One
• One-to-Many
• Many-to-One
• Many-to-Many

The various relationship types will be discussed in detail later, but here is a representation of the different relationship types:

Mandatory and optional relationships

Mandatory and optional relationships are represented with additional marks as | (line) and o (circle), respectively.

• A mandatory relationship means that an instance of one entity must be related to another entity.
• An optional relationship indicates that any instance of one entity can be related to another entity, but it is not required to do so.

Look at the examples:

Mandatory and optional relationships are used infrequently, but it is essential to know these marks.