13. Summary

The purpose of normalisation is to avoid redundant data and to make it easier to maintain a database by only having to update a record in one place only.

Characteristics of normalisation and normal forms are:

Unnormalised form (0NF)

• Data might be repeated
• Data might be non-atomic
• The table might not have a primary key
• There might be repeating fields i.e. each field does not have a unique name

First normal form (1NF)

• 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

Second normal form (2NF)

• The table must already be in 1NF
• Non-key attributes must depend on every part of the primary key

Third Normal form (3NF)

• The table must alreadybe in 2NF
• There are no non-key attributes that depend on another non-key attribute