ICT: Theory and Blockly Concepts

Bit

The smallest unit of digital data which models two possibilities (0 or 1).

They are used to model numbers.

Byte

A group of 8 bits that models 2^8 = 256 possibilities.

Files

A collection of data where bits and bytes are organized in.

File size

[Property of a file] The number of bytes within a file.

File name

[Property of a file] A unique name for a file; is usually a descriptive name of the contents.

File extension

[Property of a file] The part of the file name that indicates what is stored in the file (.pdf, .png, .mp4)

Archive files

Files that can contain multiple files.

They are useful for transporting many files and also helps to reduce file size via compression.

Software Applications

Programs (not systems) that can read, process, and write files.

Text-based Format

Designed in a way that humans can read them

Ex. HTML, CSV, XML

Binary Format

Not readable by humans but can be efficiently processed by computers

They require less space and can be processed a bit faster

Ex. videos (.mp4), images (.png), audio (.mp3)

The Internet

A network of computer networks that communicate short messages routed via many computers in the network.

Packet-switching

How communication over the Internet happens.

1. Messages are divided in small packets that are sent one by one

2. Every packet follows a different route via different computers

Properties of Packets

1. The address of a sender
2. The address of a receiver
3. Other properties related to time
4. The contents of the packet

Internet Protocol (IP) Addresses

How addresses in the internet are described

Their two main functions are:
1. Host or network interface identification
2. Location addressing

IPv4 Address

A unique 32-bit address with 2^32 different possibilities

Ex. 130.115.158.254

IPv6 Address

A unique 128-bit address with 2^128 different possibilities

Ex. fe80::c118:3329:ca70:eccc%12

Domain Name System (DNS)

The system administered by the Internet Corporation for Assigned Names (ICANN) that assigns names to each site on the Internet.

Big sites may want to rotate machines to serve customers in order to spread out demand over the available capacity.

Authentication

Checking someone's identity; knowing that you're communicating with the intended party.

Two-factor (multi-factor) authentication

An authentication method that uses multiple proofs of your identity to be able to log in

Ex. SMS, Push notifications in mobile apps

Token-based authentication

An authentication method that uses a special software/application to generate a number unique to that device.

Advanced Encryption Standard (AES)

A symmetric block cipher that is used to encrypt and decrypt messages.

The AES-256 works with keys of 256-bits.

Public Key/Certificate Encryption

A method of paired key encryption in which the key used to encrypt data is made available to anybody and its corresponding decryption key is kept secret.

Hypertext Transfer Protocol Secure (HTTPS) Protocol

An encrypted form of information transfer on the Internet that combines HTTP and a Secure Sockets Layer (SSL).

The protocol uses public keys/certificates to check whether a party you communicate with is trustworthy, then it encrypts the connection.

Redundancy

To duplicate files/software/hardware between users and/or machines to prevent or recover from the failure of a specific component or system.

Cases in which redundancy is desired

1. Archiving data

2. Having backup systems when software/hardware breaks

Cases in which redundancy is undesirable

When collaborating on a document with multiple users in which only one version must be used.

Ex. Google Docs

Synchronization

The coordination of hardware devices such that the data they contain or provide is made to be identical.

Centralization

Connecting all users to a central server/repository that stores complete and "true" network data and user information.

Conflicts that can occur when synchronizing

1. Two people modify the same file at the same time.

2. You modified a file, but it turns out another user sent a new file to the central repository in the meantime.

Local Applications

Applications that run on a local device and interact with data on that device.

Client-server Applications

Tasks and/or responsibilities are divided between a client application that typically runs on a local device and a server application that typically runs on an external server.

Ex. web browser (client application) and web server (server application)

Advantage of Client-server Applications

Data is often centralized automatically on the server.

Risk of Client-server Applications

If the server has a problem, the application is not available for any user.

Infrastructure as a Service (IaaS)

Delivers hardware networking capabilities, including the use of servers, networking, and storage, over the cloud using a pay-per-use revenue model

Platform as a Service (PaaS)

Supports the deployment of entire systems including hardware, networking, and applications using a pay-per-use revenue model

Software as a Service (SaaS)

Delivers applications over the cloud using a pay-per-use revenue model

Ex. Google Suite and Office 365 (within a browser)

Data/Source Code Escrow

If the software vendor goes bankrupt, a third party inherits the important properties and provides them to the original customers.

Expression (Blockly)

A block or group of blocks that have a value as a result.

Statement (Blockly)

A block that performs something.

Program

A sequence of instructions that specifies how to perform a computation to a computer.

[Program] Input

Getting data from a keyboard, a file, the network, some other device, etc.

[Program] Output

Displaying data on the screen, saving it in a file, sending it over the network, etc.

[Program] Math

Performing basic mathematical operations such as addition and multiplication.

[Program] Repetition

Performing some action repeatedly, usually with some variation.

[Program] Conditional Execution

Checking for certain conditions and running the appropriate code.

Print Statement

An instruction that causes Blockly to display a value on the screen.

Operator Blocks

Special blocks in Blockly that represent computations like addition, multiplication, or string concatenation.

Variable

A name that refers to a value.

Operand

An element that identifies one of the values on which an operator operates.

[Function block] Header

The name of the function and which possible input can be given.

[Function block] Body

The sequence of statements that make up/are within the function block.

[Function block] Parameter

A name used inside a function to refer to the value passed as an argument.

[Function Block] Argument

A value provided to a function when the function is called.

This value is assigned to the corresponding parameter in the function.

Logical Operator

One of the operators that combines boolean expressions: and, or, and not.

Relational Operator

Used to compare two values. Operators include =,

Branches of a Conditional Statement

The different alternatives of a conditional statement.

Ex. else if, else

Flow of Execution

The order in which statements are executed during a program run, which in Blockly is from top to bottom.

Fruitful Function

A function that returns a result.

Void Function

A function that performs an action but does not return a value.

Runtime errors

Errors that occur while your program runs.

Semantic errors

Errors that occur as a result of an incorrect output, despite the working program.

Numeric data

Type of data that is formatted as numbers and can be used in a calculation.

Textual/string data

Type of data that is formatted as a string; letters, symbols, numbers.

Boolean data

Type of data that is formatted as "truth" values; true or false.

Dictionary Attack

A password attack that creates encrypted versions of common dictionary words and compares them against those in a stolen password file.

Brute Force attack

An attack on passwords or encryption that tries every possible password or encryption key.