Normalization is a method for organizing data into tables.

Normalization help us to 

1. Duplication of Data
The same data listed in multiple lines of the database avoided.

2. Insert Anomaly
A record about an entity cannot be inserted into the table without first inserting information about another entity

Cannot enter test marks without entering student name

4. Delete Anomaly
A record cannot be deleted without deleting a record about a related entity.

Cannot delete a customer without deleting all sales orders

Cannot update information without changing information in many places.
When updating customer addresses, each sales order by the customer has to be updated.

Normalization is a three-stage process

• After the first stage, the data is said to be in first normal form (1nf)
• After the second (2nf), it is in second normal form
• After the third, it is in third normal form (3nf)
  
  
  

Before Normalization 

• Begin with a list of all of the fields that must appear in the database.
• Think database as one big table with all columns in it.
• Do not include computed fields total salary = basic + allowance)
• Begin getting data fields is from document used by the manual system.
• Additional attributes identified on document added to the database.

Invoices, purchase orders, receipts, Customer Lists, Payment Vouchers

A Normalized Example