1.3 Exchanging data

Question 1

Lossy compression

Answer 1

Reduces file size by permanently removing data; not reversible; e.g., JPEG, MP3.

Question 2

Lossless compression

Answer 2

Reduces file size without losing data; reversible; e.g., PNG, ZIP.

Question 3

Run Length Encoding (RLE)

Answer 3

Replaces repeated consecutive characters with count + value (e.g., WWWWW -> 5W).

Question 4

Dictionary coding

Answer 4

Replaces frequently occurring patterns with index references to a dictionary (e.g., LZW, GIF).

Question 5

Symmetric encryption

Answer 5

Same key used for encryption and decryption; fast; problem = key exchange (e.g., AES).

Question 6

Asymmetric encryption

Answer 6

Public key encrypts, private key decrypts; slower; used for key exchange/digital signatures (e.g., RSA).

Question 7

Use of hashing

Answer 7

One-way function; verify integrity; store passwords; digital signatures.

Question 8

Primary key

Answer 8

Uniquely identifies a record in a table.

Question 9

Foreign key

Answer 9

Field in one table that references the primary key in another table; establishes relationship.

Question 10

Secondary key

Answer 10

An indexed field used for searching that is not unique (e.g., searching customers by surname).

Question 11

Entity Relationship (ER) modelling

Answer 11

Diagram showing entities, attributes, and relationships between entities.

Question 12

Normalisation

Answer 12

Process of organising data to reduce redundancy and improve integrity.

Question 13

First Normal Form (1NF)

Answer 13

No repeating groups; atomic values; primary key identified.

Question 14

Second Normal Form (2NF)

Answer 14

1NF + No partial dependencies (non-key attributes depend on whole primary key).

Question 15

Third Normal Form (3NF)

Answer 15

2NF + No transitive dependencies (non-key depends on non-key).

Question 16

Indexing

Answer 16

Improves speed of data retrieval; uses additional storage; slows down INSERT/UPDATE/DELETE.

Question 17

Referential integrity

Answer 17

Ensures foreign key values match a valid primary key; prevents orphan records.

Question 18

ACID acronym

Answer 18

Atomicity, Consistency, Isolation, Durability (properties of database transactions).

Question 19

Atomicity

Answer 19

Transaction is all-or-nothing; if one part fails, whole transaction rolls back.

Question 20

Consistency

Answer 20

Transaction brings database from one valid state to another; constraints maintained.

Question 21

Isolation

Answer 21

Concurrent transactions do not interfere; appear as if executed serially.

Question 22

Durability

Answer 22

Once committed, transaction persists even after system failure.

Question 23

Record locking

Answer 23

Prevents two users from editing the same record simultaneously.

Question 24

Redundancy (database)

Answer 24

Duplication of data; normalisation removes it; can also refer to backup copies for fault tolerance.

Question 25

SQL: SELECT

Answer 25

Retrieves data from a database.

Question 26

SQL: SELECT with multiple tables

Answer 26

Can retrieve data from multiple tables using JOIN or subqueries.

Question 27

SQL: Nested SELECT

Answer 27

A SELECT query within another SELECT query (inner query executes first).

Question 28

SQL: FROM

Answer 28

Specifies which table(s) to retrieve data from.

Question 29

SQL: WHERE

Answer 29

Filters records based on a condition.

Question 30

SQL: LIKE

Answer 30

Used in WHERE clause for pattern matching.

Question 31

SQL: AND

Answer 31

Combines multiple conditions; all must be true.

Question 32

SQL: OR

Answer 32

Combines multiple conditions; at least one must be true.

Question 33

SQL: DELETE

Answer 33

Removes records from a table.

Question 34

SQL: INSERT

Answer 34

Adds new records to a table.

Question 35

SQL: DROP

Answer 35

Deletes an entire table or database structure.

Question 36

SQL: JOIN (INNER JOIN)

Answer 36

Returns records where the join condition matches in both tables.

Question 37

SQL: Wildcard `*`

Answer 37

Selects all columns.

Question 38

SQL: Wildcard `%`

Answer 38

Represents zero or more characters in LIKE (e.g., `WHERE name LIKE 'A%'`).

Question 39

SQL: Wildcard `_`

Answer 39

Represents a single character in LIKE (e.g., `WHERE name LIKE 'A_'`).

Question 40

TCP/IP Stack layers (top to bottom)

Answer 40

Application, Transport, Internet, Link.

Question 41

What does DNS do?

Answer 41

Converts domain names (google.com) into IP addresses (142.250.180.46).

Question 42

Packet switching

Answer 42

Data split into packets; each packet routes independently; efficient; no fixed path.

Question 43

Circuit switching

Answer 43

Dedicated communication path established for duration of call (e.g., traditional telephone).

Question 44

Client-server network

Answer 44

Central server provides services; clients request; centralised control.

Question 45

Peer-to-peer (P2P) network

Answer 45

No central server; each node acts as client/server; decentralised (e.g., BitTorrent).

Question 46

What is a NIC?

Answer 46

Network Interface Card; hardware that connects a device to a network (MAC address).

Question 47

What is a switch?

Answer 47

Connects devices within a LAN; uses MAC addresses to forward data only to destination.

Question 48

What is a router?

Answer 48

Connects different networks (e.g., LAN to WAN); uses IP addresses; forwards packets between networks.

Question 49

What is a bridge?

Answer 49

Connects two LAN segments; filters traffic based on MAC addresses.

Question 50

What is a gateway?

Answer 50

Connects networks using different protocols; translates between them.

Question 51

What is a firewall?

Answer 51

Monitors and controls incoming/outgoing traffic based on security rules.

Question 52

What is a proxy server?

Answer 52

Intermediary between client and destination; hides client IP; can cache content; filter requests.

Question 53

HTML purpose

Answer 53

Structure and content of a webpage.

Question 54

CSS purpose

Answer 54

Stlying and layout of a webpage.

Question 55

JavaScript purpose

Answer 55

Adds interactivity/dynamic behaviour to a webpage.

Question 56

How do search engines index?

Answer 56

Web crawlers/spiders follow links; parse content; store keywords/metadata in an index database.

Question 57

PageRank algorithm

Answer 57

Google algorithm; ranks pages based on number/quality of inbound links.

Question 58

Server-side processing

Answer 58

Code runs on web server (e.g., PHP, Python); generates dynamic HTML.

Question 59

Client-side processing

Answer 59

Code runs in user's browser (e.g., JavaScript); reduces server load.