Unit 2 - Normalisation

Question 1

What is Normalisation?

Answer 1

A technique of organising the data in a database into multiple, separate related entities (tables) to minimise Data Redundancy

Question 2

What is Data Redundancy?

Answer 2

The duplication of similar data in multiple places which causes problems (loss of data integrity)

Question 3

What are the three types of problems that data redundancy may cause?

Answer 3

Insertion anomalies
Deletion anomalies
Update/modification anomalies

Question 4

Explain the three types of anomalies that data redundancy may cause

Answer 4

Insertion anomalies:
As we insert/add more employee’s data, we are inserting redundant data
We have two different but related data store in the same entity (table)

Deletion Anomalies:
If we delete employee information, we will also delete Department information simultaneously
If all employee information are deleted we also unintentionally delete all department information

Update/modification Anomalies:
The Head of Department’s name will have to be changed hundreds of times
This creates a lot of unnecessary work
If even one record is missed out it will lead to inconsistent data
So data redundancy can also lead to inconsistency in data as a result of update/modification anomalies