One-to-one (1:1)
- This is where an occurrence of an entity relates to just one occurrence in another entity.
- Example: An employee is allotted an organization vehicle, which is driven by that employee only. Therefore, there’s a one-to-one relationship between employee and company vehicle.
Clarification of 1:1
An Employee is allotted only one Vehicle.
A Vehicle is also allotted to only one Employee.
One-to-Many (1:M)
- In this relationship, one occurrence of an entity relates to many occurrences in another entity.
- Example: an employee works in one department however a department has several employees. Therefore, there’s a one-to-many relationship between department and employee.
Clarification of 1:M
A Department has many Employees.
An Employee works in only one Department.
Many-to-Many (M:N)
- This is where several occurrences in an entity relate to several occurrences in another entity.
- Example: An employee works on many projects and at the same time, a project has several employees. This many-to-many relationship can be seen between project and employee.
Clarification of M:N
A Project has many Employees.
An Employee works on many Projects.
