Relationship in DBMS-
Before you go through this article, make sure that you have gone through the previous article on Introduction to ER Diagrams.
|A relationship is defined as an association among several entities.|
‘Enrolled in’ is a relationship that exists between entities Student and Course.
Also read- Entity Sets in DBMS
A relationship set is a set of relationships of same type.
Set representation of above ER diagram is-
Degree of a Relationship Set-
The number of entity sets that participate in a relationship set is termed as the degree of that relationship set. Thus,
|Degree of a relationship set = Number of entity sets participating in a relationship set|
Types of Relationship Sets-
On the basis of degree of a relationship set, a relationship set can be classified into the following types-
- Unary relationship set
- Binary relationship set
- Ternary relationship set
- N-ary relationship set
1. Unary Relationship Set-
Unary relationship set is a relationship set where only one entity set participates in a relationship set.
One person is married to only one person
2. Binary Relationship Set-
Binary relationship set is a relationship set where two entity sets participate in a relationship set.
Student is enrolled in a Course
3. Ternary Relationship Set-
Ternary relationship set is a relationship set where three entity sets participate in a relationship set.
4. N-ary Relationship Set-
N-ary relationship set is a relationship set where ‘n’ entity sets participate in a relationship set.
Next Article- Cardinality in ER Diagram
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