Entity Relationship Participation in Database

DatabaseMCARDBMS

In a Relationship, Participation constraint specifies the existence of an entity when it is related to another entity in a relationship type. It is also called minimum cardinality constraint.

This constraint specifies the number of instances of an entity that can participate in a relationship type.

There are two types of Participation constraint −

Total Participation

Each entity in the entity set is involved in at least one relationship in a relationship set i.e. the number of relationship in every entity is involved is greater than 0.

Consider two entities Employee and Department related via Works_For relationship. Now, every Employee works in at least one department therefore an Employee entity exist if it has at least one Works_For relationship with Department entity. Thus the participation of Employee in Works_For is total relationship.

Total Participation is represented by double line in ER diagram.

Partial Participation

Each entity in entity set may or may not occur in at least one relationship in a relationship set.

For example: Consider two entities Employee and Department and they are related to each other via Manages relationship. An Employee must manage a Department, he or she could be the head of the department. But not every Employee in the company manages the department. So, participation of employee in the Manages relationship type is partial i.e. only a particular set of Employees will manage the Department but not all.

raja
Published on 23-Jul-2018 12:32:07
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