4.10.3 Database Design & Normalisation

Why are databases normalised?

So that they can be efficient without compromise to the integrity of their data

How are databases normalised?

Redundant or repeated data is removed from entities

What does normalisationn allow for?

- Faster searching and sorting

- Easier maintenance

- Improved data consistency

- Minimised duplication

- Reduced number of update, insertion and deletion anomalies

What are the three levels of normalisation?

- First normal form

- Second normal form

- Third normal form

What happens when a data base conforms to first normal form?

It contains no repeating attributes

→ Data is referred to as atomic

What happens when a database conforms to second normal form?

- Satisfies first normal form

- Partial key dependencies are removed

When do partial key dependencies occur?

In databases with composite primary keys when a non-key attribute does not depend on the whole of the composite key

What happens when a database conforms to third normal form?

- Conforms to second normal form

- Must have no non-key dependencies