3. First Normal Form - 1NF

For a database to be in first normal form (1NF), the following rules have to be met for each table in the database

• There are no columns with repeated or similar data
• Each data item cannot be broken down any further.
• Each row is unique i.e. it has a primary key
• Each field has a unique name

'Atomic' is the word used to describe a data item that cannot be broken down any further.

Examples of atomic data

• An identity number
• National Insurance number NY344599
• ISBN book reference e.g.1-931841-62-4
• Stock code PN10B
• A first name, 'John'
• A surname, 'Hunt'
• A telephone number
• A school name: 'Abington Hall Comprehensive School'
• A complete description 'A fountain pen is a writing instrument'.

The point of the two last examples indicates that 'atomic' does not mean 'single word'. It simply means that it would make no sense to reduce the data item any further as it would lose its meaning.

Examples of non-atomic data

• A full name: John Hunt when a first name and surname is present in the database
• A full address: 6 Picton Road, London, WR1 4PG
• Data that are part of a larger dataset e.g Oxford Book club and Coventry Health club

In the last example, the database in question is storing club details and there are many different kind of clubs (Health, Book, Chess etc) being stored. So it would make sense to split this data into {Location, Club type}. So the context of the database needs to be understood when deciding if data is atomic or not.

Example of repeating data

In this case the database is trying to store contact telephone numbers for each person. The designer has created three fields to hold telephone numbers. This is what is meant by 'repeating data'. The telephone numbers are the same kind of data.