1.3 Exchanging Data

Question 1

Define and explain lossy compression

Answer 1

Lossy compression is a way of reducing the file size by deleting irrelevant data. The data is lost and the original cannot be recreated. This reduces the quality

Question 2

Define and explain lossless compression

Answer 2

Data from the file is not lost and the original can be easily recreated. Records patterns in the data and stores instructions on how to recreate the file

Question 3

What is run length encoding?

Answer 3

Used with images. The data can be stored as a list of colours, counting the number of repeating patterns

Question 4

What is dictionary coding?

Answer 4

Used mainly for text and software applications where no data is irrelevant. The data is stored in a dictionary style. The word is stored once and referenced to reduce the amount of data stored.

Question 5

What is the difference between symmetric and asymmetric encryption?

Answer 5

symmetric - if the key is intercepted the message is easily de-cryptable as the same key is used to encrypt and decrypt the data
Asymmetric - a user has a private and public key which is unique, the user only ever sends the public key to encrypt a message and decrypts the message using the private key which is never sent

Question 6

What is encryption?

Answer 6

The process of encoding the message so that it can only be read by the sender and the intended recipient.

Question 7

What is an encryption key?

Answer 7

The data is encrypted using an encryption key. If the data is intercepted, it cannot be deciphered unless they have the key.

Question 8

What is hashing?

Answer 8

Data is converted into a number or string similar to encryption however the data is unable to be converted back to its original input. If the output is the same you can assume that the passwords match.

Question 9

What is the difference between encryption and hashing?

Answer 9

Encryption makes a message unreadable to users that should not be allowed access unless they have the key whereas hashing coverts an input into an output and cannot be reversed. Can be used for checking and storing passwords as well as determining where to store data i.e. hash tables

Question 10

What is a hash function?

Answer 10

Used to generate the output. The output will be the same every time a string is entered providing you enter the same string each time.

Question 11

Define what a relational database is

Answer 11

a database that links tables through primary and foreign keys including attributes and entities

Question 12

Define what a flat file database is

Answer 12

made as lists like a spreadsheet. Flat file databases are often prone to data redundancy however they are fine for small amounts of data

Question 13

Define primary key

Answer 13

unique identifier of an entity

Question 14

Define what an entity relationship diagram is

Answer 14

A data modelling diagram technique used to define a relational database

Question 15

What is database normalisation?

Answer 15

Organising attributes and relations of a relational database to minimise data redundancy

Question 16

What is database indexing?

Answer 16

Used to speed up searching. sequentially searches through the data. Like an index in a book

Question 17

What are the rules of 1NF?

Answer 17

Remove duplicate data

Needs a primary key

Question 18

What are the rules of 2NF?

Answer 18

Must be in 1NF
A composite key is usually created
Remove data sets that occur in multiple rows

Question 19

What are the rules of 3NF?

Answer 19

Must be in 2NF

All data has to rely on the primary key

Question 20

What is SQL?

Answer 20

Structured Query Language - used to communicate and create databases

Question 21

Name 3 SQL commands and explain what they do

Answer 21

SELECT
DELETE
UPDATE

Question 22

What is meant by referential integrity?

Answer 22

Adds constraints to the data updated, deleted and entered into a relational database to ensure that the data is as accurate as possible uses cascade updates and prevents deletion of a record that is a foreign key of another table

Question 23

What is ACID?

Answer 23

Atomicity
Consistency
Isolation
Durability
A set of properties to ensure that the integrity of the database is maintained under all circumstances. It guarantees that transactions are processed reliably

Question 24

What is atomicity?

Answer 24

Requires a transaction to be processed in its entirety or not at all. It makes it impossible to process only part of a transaction

Question 25

What is consistency?

Answer 25

Ensures that no transaction can violate any of the validation rules. Therefore referential integrity will always be upheld

Question 26

What is isolation?

Answer 26

Ensures that the execution of transactions leads to the same results as if they were processed one after another. Crucial in a multi-user database

Question 27

What is durability?

Answer 27

Ensures that once a transaction has been committed, it remains even in the even of a power cut. As each part of the transaction is completed, it is held in a buffer on a disk until all elements are completed. Only then will changes be made to the database.

Question 28

What is a multi-user database?

Answer 28

allows multiple users to simultaneously access a database. This could potentially cause updates to be lost if more than one user is editing the database at a time

Question 29

What is record locking?

Answer 29

Prevents simultaneous access to the database to prevent updates being lost or inconsistencies in the data arising. However if two users are attempting to update two records deadlock can occur

Question 30

What is serialisation?

Answer 30

Prevents deadlock. This ensures that the transactions do not overlap in time and therefore cannot interfere with each other or lead to updates being lost.

Question 31

What is timestamp ordering?

Answer 31

Every object in the database has a read and write timestamp. These are updated whenever an object is written or read. When a user tries to save an update the DBMS knows that another user has accessed the object is the timestamp is not the same as when they started

Question 32

What is database redundancy?

Answer 32

What a part of the system fails, the machine becomes redundant. We can create duplicate hardware that mirrors every transaction that takes place and can automatically take over if the main system fails

Question 33

Why is it important that networks have protocols and standards?

Answer 33

Protocols are rules and standards that govern data transmission. They ensure that devices can talk to each other. 4 layers
Application - concerned with production and reception of data. Packages data and passes to transport layer
Transport - makes and breaks connections via routers
Internet - Provides links across different network types
Link - Passes data to the physical network.

Question 34

Describe the TCP/IP stack

Answer 34

Transmission Control Protocol/ Internet Protocol - Used to bring order to the internet as well as many private networks.

Question 35

What is meant by a client-server network?

Answer 35

High end computers acting as servers which provide service to the users/clients. This includes; file storage and access, printing, internet access and security features. Adds more control over the network

Question 36

What is meant by a peer to peer network?

Answer 36

Each computer has an equal status. It is generally cheap and not a very common way of implementing a network. Easy to pass files between the users without having to go through a server. Can make use of distributed computing for collaborative working

Question 37

What is HTML?

Answer 37

HyperText Markup Language - a text-based language that uses tags, producing basic web pages using any plain text editor

Question 38

What is CSS?

Answer 38

Cascading Style Sheets - Defines how HTML elements are to be displayed. CSS files are stored separately from the HTML they affect

Question 39

What is JavaScript?

Answer 39

Adds interactivity into a webpage