In addition it would be a good idea to give each DVD a serial number to identify each uniquely. This is because it is possible for more than one film to have the same name. (Check out Cape Fear, made in 1962 and remade in 1991). This unique number we usually refer to as the "Key".
This is an important concept. Let us look at several examples:
- Each item in the supermarket has a bar-code, The bar code represents the product-code. The product-code is the key of the item in the database.
- Your telephone has a unique number which no-one else has. This is the key of your phone's record held by your service provider.
- At work you will usually be known by your name. But it is essential to uniquely identify each employee individually since more than one person can have the same name. This is usually implemented be allocating each employee an Employee Number. This is the key of your employee record.
For the following items list the information we would store for each and identify the key for each.
- Each product in the supermarket
- Each employee in the organisation
- Patient details at your doctor's surgery
Student details for each student in a college