Exchanging Data- S4

Question 1

Compression

Answer 1

reduce the storage space of files on disk.

Question 2

Why is compressing important?

Answer 2

Compression is Important when transmitting data as Internet Service Providers often have limits. Images on websites need to be compressed to enable the web site to load quickly to reduce buffering.

Question 3

Lossy compression

Answer 3

non-essential information is removed from the original file.

Question 4

Lossless compression

Answer 4

retains all information required to replicate the original file exactly.

Question 5

Entity

Answer 5

is a category of object, person, event or thing of interest to an organisation about which data is to be recorded. (E.g Employee, Actor, Product).

Question 6

Attribute

Answer 6

a property or characteristic of an entity.

Question 7

Flat file database

Answer 7

consists of a single file (one entity).

Question 8

Relational database

Answer 8

different entities in a system may be linked in some way, and the two entities are said to be related.

Question 9

Primary Key

Answer 9

An entity’s unique identifier, normally a numeric ID.

Question 10

Secondary Key

Answer 10

An index so that something can be quickly searched up. It would be quicker to search a secondary key like a name than a primary key ID.

Question 11

Index

Answer 11

so that a record can be quickly located in the database an index is maintained so that it will give the position of each record. Primary keys and other things that are often searched (secondary keys) are indexed.

Question 12

Foreign Key

Answer 12

the attribute that links the two entities/table (attribute that is common in both tables, can be more than one.)

Question 13

Composite Primary Key

Answer 13

A primary key which consists of more than one attribute. (used when there is a many to many relationship between entities.)

Question 14

Referral integrity

Answer 14

states relationships must be consistent, so when a primary key field changes so does the foreign key that has the link. And ensuring a primary key that is responsible for the link is not deleted

Question 15

Normalisation

Answer 15

a process used to come up with the best possible design for a relational database.

Question 16

Give some rules of Normalisation

Answer 16

No data is unnecessarily duplicated
Data is consistent throughout the databases.
The structure should be flexible enough to allow you to enter as many or as few items as required
The structure should enable a user to make complex queries relation data from different tables.