Relationship

Degree of Relationship

The degree of a relationship is the number of entity types that participate(associate) in a relationship.

• Unary Relationship

• Binary Relationship

• Ternary Relationship

• N-ary Relationship

Cardinality of Relationship

One to One – A single row of first table associates with single row of second table. For example, a relationship between person and passport table is one to one because a person can have only one passport and a passport can be assigned to only one person.

One to Many – A single row of first table associates with more than one rows of second table. For example, relationship between customer and order table is one to many because a customer can place many orders but a order can be placed by a single customer alone.

Many to One – Many rows of first table associate with a single row of second table. For example, relationship between student and university is many to one because a university can have many students but a student can only study only in single university at a time.

Many to Many – Many rows of first table associate with many rows of second table. For example, relationship between student and course table is many to many because a student can take many courses at a time and a course can be assigned to many students.