Databases

Question 1

What is a flat file?

Answer 1

A database that consists of a single file/table.
Based around a single entity and it’s attributes.

Question 2

What is a disadvantage of a flat file?

Answer 2

Lead to duplication/redundancy if second user entries need to be recorded.
Can lead to inconsistency - database becomes inconsistent in it’s use before repeated value occurred.

Question 3

What is a record?

Answer 3

Row - Collection of fields about the same entity in a database

Question 4

What is a field?

Answer 4

Individual attributes about same entity in a database

Question 5

What is an entity?

Answer 5

A category of a person/real world object/event where data needs to be recorded

Question 6

What is a primary key?

Answer 6

Unique identifier of a record in a table eg. customerID

Question 7

What is secondary key

Answer 7

Allows a database to be searched quickly as it can be used as a search term/query

Question 8

What are the entity relationship models

Answer 8

One to many
Many to Many
One to one

Question 9

What is database normalisation aimed to do

Answer 9

Reduce inconsistencies
Reduce redundancies

Question 10

Three types of normalisation and characteristics

Answer 10

First normal form (USA)
-Has a primary key
-Atomic values (non divisible, just one value)
-Single value

Second normal form
-should be in 1nf
-no partial dependencies

3NF
-should be in 1nf,2nf
-no transitive/non key dependencies - attribute should only depend on primary key not each other

Question 11

What are the seven commands SQL can do

Answer 11

ORDER BY
UPDATE
DELETE
CREATE
JOIN
INSERT INTO
ALTER

Question 12

What is referential integrity?

Answer 12

Process of ensuring consistency
Ensures data is not removed if required elsewhere in a linked database

Question 13

What is ACID?

Answer 13

Atomic - A transaction should be processed fully otherwise it wont be recorded
Consistency - any changes should not break the database, must be consistent with how it was before the change.
Isolation - transactions should be isolated and not interfere with another transaction
Durability - a transaction must remain in the database

Question 14

What is data integrity?

Answer 14

Accuracy and reliability of data in a computer system

Question 15

What is record locking?

Answer 15

Process of preventing simultaneous access to records so theyre not accessed at the same time