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Relationship of higher degree in DBMS

 

The number of occurrences in one entity, which is correlated with the times of events in another entity defines the degree of relationship.

There is a three degree of relationship:

  1. One-to-one (1:1)
  2. One-to-many (1: M)
  3. Many-to-many (M: N)

 

One-to-one

  • According to the One-to-one relationship, anyone occurrence in the entity is related to exclusively one occurrence in other entity.
  • However, One-to-one relationship is not commonly seen in practice.
  • For instance, if an employee is provided a vehicle by the company, then the vehicle shall be only driven by the respective employee.
  • Hence, the vehicle of the company and employee is sharing a one-to-one relationship.

 

One-to-Many

  • One-to-many occurrence refers to one occurrence in any entity that is related to many incidents in other entity.
  • For instance, Any employee works in any one department. However, any department can have various employees.
  • Hence, the employee and department have a one-to-many relationship.

 

Many-to-many

  • Many-to-many degree of relationship refers to the various occurrences in any entity which relates to many other phenomena in another entity.
  • Many-to-many degree of relationship is similar to a one-to-one relationship. Many-to-many relationship hardly exists in a system.
  • For instance, an employee can do work on various projects. Any project can have a large team of multiple employees.
  • Hence, project and employee maintain a many-to-many relationship.
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