Participation Constraints | DBMS

Participation Constraints-

 

Before you go through this article, make sure that you have gone through the previous article on Introduction to ER Diagrams.

 

Participation constraints define the least number of relationship instances in which an entity must compulsorily participate.

 

Types of Participation Constraints-

 

There are two types of participation constraints-

 

 

1. Total participation
2. Partial participation

 

1. Total Participation-

 

• It specifies that each entity in the entity set must compulsorily participate in at least one relationship instance in that relationship set.
• That is why, it is also called as mandatory participation.
• Total participation is represented using a double line between the entity set and relationship set.

 

 

Example-

 

 

Here,

• Double line between the entity set “Student” and relationship set “Enrolled in” signifies total participation.
• It specifies that each student must be enrolled in at least one course.

 

Also read- Relationship Sets in DBMS and Entity Sets in DBMS

 

2. Partial Participation-

 

• It specifies that each entity in the entity set may or may not participate in the relationship instance in that relationship set.
• That is why, it is also called as optional participation.
• Partial participation is represented using a single line between the entity set and relationship set.

 

 

Example-

 

 

Here,

• Single line between the entity set “Course” and relationship set “Enrolled in” signifies partial participation.
• It specifies that there might exist some courses for which no enrollments are made.

 

Relationship between Cardinality and Participation Constraints-

 

Minimum cardinality tells whether the participation is partial or total.

• If minimum cardinality = 0, then it signifies partial participation.
• If minimum cardinality = 1, then it signifies total participation.

Maximum cardinality tells the maximum number of entities that participates in a relationship set.

 

Next Article- Types of Attributes in DBMS

 

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