Degree of a Relationship

The number of participating entities in a relationship is known as the degree of the relationship.

If there are two entity types involved it is a binary relationship type
If there are three entity types involved it is a ternary relationship type
It is possible to have a n-array relationship (e.g. quaternary or unary).
Unary relationships are also known as a recursive relationship.
It is a relationship where the same entity participates more than once in different
In the example above we are saying that employees are managed by employees.
If we wanted more information about who manages whom, we could introduce a
second entity type called manager.