DB+-+Relationships

__**Relationships**__ by Gary :)

When a DVD is rented, a link is made between a DVD rental and member, this is called a relationship. Each member can rent out many DVDs but each DVD can only be rented by one member at a time, so we say there is a one-to-many relationship between member DVD rental


 * 1:M - Stands for one-to-many.**

There are other types of relationship between entites, for example, every vehicle has a registration number, and each registration number corresponds to a single vehicle, so there is a one-to-one relationship between vehicle and registration number.


 * 1:1 - Stands for one-to-one**.

In a school, every pupil has many teachers, and each teacher teaches many pupils, so there is a many-to-many relationship between pupil and teacher.


 * M:N - Stands for many-to-many (the number of teachers and pupils may be different, which is why N is used instead of M)**.


 * __Data Modelling__**

Data Modeling is the process of defining the entites, attributes and relationships that are required, the result is called a data model.