Lesseon 6 One to One

Three type of relationship exist among entities
These are:
a) One to one (1:1)
b) One to many (1:m)
c) Many to many (m:m)

a) One to one (1:1)
A one to one (1:1) relationship is an association only between two entities.
For example, in a university each department has only one head of department. More over one faculty member cannot be the head of more than one department.
This shows one to one relationship between departments as head.
Another example of such relationships is between automobile & engine. If we assume that a car does not have two engines and that car must be filter with one engine in car.