What is meant by a recursive relationship type? Give some examples of recursive relationship types.
The correct answer and explanation is :
Recursive Relationship Type
A recursive relationship type is a relationship where an entity in a database is related to itself. This means that the same entity type plays different roles in the relationship. It is also called a unary relationship because it involves only one entity set.
Explanation
In an Entity-Relationship (ER) Model, entities are connected through relationships. A recursive relationship is when a single entity participates multiple times in the same relationship, playing different roles. This is useful when an entity has a hierarchical or self-referential structure.
For example, in a company:
- Employee (entity) can have a recursive relationship “manages” where:
- One employee is a manager.
- Another employee is a subordinate.
This means an employee can manage another employee, creating a hierarchical structure.
Examples of Recursive Relationships
- Employee-Manages-Employee: An employee manages another employee.
- Person-Is Parent Of-Person: A person can be a parent of another person.
- Course-Prerequisite-Course: A course may have another course as a prerequisite.
- Folder-Contains-Folder: A folder can contain other subfolders in a file system.
- User-Follows-User: In a social media platform, one user can follow another user.
Recursive relationships are important in database design for handling hierarchical and self-referencing data.
Recursive relationship in an ER diagram:
Here is an ER diagram illustrating a recursive relationship where an “Employee” manages another “Employee”. This type of relationship helps model hierarchical structures in databases.