4.10 - Fundamentals of databases

Question 1

Why are databases normalised?

Answer 1

So that they can be efficient without any compromise to the integrity of the data. It involves ensuring that entities contain no redundant or repeated data.

A normalised database allows faster searching and sorting thanks to smaller tables.

Easier to maintain

Duplication of data minimised and data consistency improved, helping to reduce number of update, insertion and deletion anomalies that occur.

Question 2

What is first normal form?

Answer 2

When there are no repeating attributes

Question 3

What is second normal form?

Answer 3

When there are no partial key dependencies - every attribute is dependent on the whole key.

Question 4

What is third normal form?

Answer 4

When there are no non-key dependencies.

All non-key attributes depend on the key, the whole key and nothing but the key.

Question 5

What is concurrent access?

Answer 5

When two or more different users in a client server database system attempt to access the same field at the same time.

Question 6

How do record locks work?

Answer 6

When a record is accessed by one user it is immediately locked to other users until the first user finishes using it.

Question 7

How does serialisation work?

Answer 7

Requests from other users are placed in a queue. Once the first user has finished using the field, the next command in the queue is executed.

Question 8

How does timestamp ordering work?

Answer 8

Each command assigned a timestamp which marks point in time at which command was initiated. Commands then carried out in order of timestamps.