10 - Fundamentals of Databases

Question 1

What does it mean for relations to be in Third Normal Form.

Why is it important that the relations in a relational database are in Third Normal Form?

Answer 1

3NF means every non-key attribute is dependent on the key, the whole key and nothing but the key. There are also no repeating groups.

This is important to eliminate update anomalies, eliminate insertion anomalies, eliminate deletion anomalies, eliminate data inconsistency and minimise data duplication.

Question 2

State the properties that the relations in a fully normalised database must have.

Answer 2

• There are no repeating groups of attributes.
• All non-key attributes depend on the whole key.
• All non-key attributes depend on nothing but the key.

Question 3

Describe a problem when a table is not normalised.

Answer 3

It is difficult to query as it contains repeating groups of attributes.

Question 4

What is the name given to a key that is made up of multiple attributes?

Answer 4

Composite key

Question 5

Why is it important for a database to be in third normal form?

Answer 5

• Eliminate update anomalies
• Eliminate insertion anomalies
• Eliminate deletion anomalies
• Eliminate data inconsistency
• Eliminate data redundancy