1.3.2 Databases

Question 1

In the ACID acronym for transaction processing, what does the A stand for, and what does it mean?

Answer 1

Atomicity-
The concept that the components of a transaction are atomic, i.e. indivisible. The whole transaction must succeed or fail.

Question 2

In the ACID acronym for transaction processing, what does the C stand for, and what does it mean?

Answer 2

Consistency-

Ensures that an illegal transaction is rejected so that the integrity of the database is upheld.

Question 3

In the ACID acronym for transaction processing, what does the I stand for, and what does it mean?

Answer 3

Isolation-

Ensures that each transaction will be isolated and dealt with in a way that does not affect others.

Question 4

In the ACID acronym for transaction processing, what does the D stand for, and what does it mean?

Answer 4

Durability-
Ensures that data is saved once a transaction has been completed. Even if there is a hardware failure immediately after a transaction, the data will be safe.

Question 5

What is Serialisation?

Answer 5

Serialisation is the concept that, when two or more transactions are executed concurrently, the effect should be the same as if they had been executed serially

Question 6

What is a technique that will allow transactions to be run at the same time, preventing them from interfering with each other?

Answer 6

Record locking

Question 7

What does DMBS stand for?

Answer 7

DMBS stands for Database Management System, and is essentially nothing more than a computerized data-keeping system

Question 8

What is record locking?

Answer 8

Record locking is a common method to allow concurrent transactions. The DBMS will lock the affected record until the update is completed

Question 9

What is deadlocking?

Answer 9

Deadlocking is a state in which each member of a group waits for another member, including itself, to take action, such as sending a message or more commonly releasing a lock

Question 10

What can the SQL command SET TRANSACTION do?

Answer 10

It can be used to initiate a database transaction

Question 11

What does a COMMIT statement do in transactions?

Answer 11

A COMMIT statement will make the changes of a transaction permanent

Question 12

What does ROLLBACK do in transactions?

Answer 12

it reverts any interim changes to the point prior to the transaction being started

Question 13

What does SAVEPOINT do in transactions?

Answer 13

It creates a save point mid-transactions, meaning the changes can be partially rolled back instead of back to the start

Question 14

What is normalisation?

Answer 14

Normalisation is a technique used to help reduce data duplication when designing data structures, also resulting in an improvement in data integrity

Question 15

What is dependancy?

Answer 15

A value that varies in line with another value

Question 16

What is the criteria of data being in First Normal Form (1NF)?

Answer 16

Each record must have a primary key
The data in each field (column) must be atomic
Each record must have no repeating groups of attributes

Question 17

What is the rule for Second Normal Form? (2NF)

Answer 17

The rule for 2NF is no partial dependencies

Question 18

What is the rule of the Third Normal Form? (3NF)

Answer 18

There must be no non-key dependencies

Question 19

What is a non-key dependancy?

Answer 19

there are no fields that are dependent on other fields that are not part of the key

Question 20

What is a functional dependancy?

Answer 20

A set of constraints between two attributes in a relation

Question 21

What is a partial dependency?

Answer 21

Partial dependencies arise where a table has a composite key