1.2.2 - Applications Generation

Question 1

Describe and give examples of application software

Answer 1

Performs generic tasks for the user
Examples:
- Database (DBMS)
- Word processor
- Spreadsheet
- Graphics editor
- Desktop Publisher (DTP)
- Presentation Software
- Computer Aided Design (CAD)

Question 2

Which category of software would be used to perform each of the following tasks?

Answer 2

Question 3

Describe and give examples of utility software

Answer 3

A piece of system software, with one specific purpose, that is used for the maintenance of the system

Examples:
- Disk Defragmenter - puts fragmented files in consecutive storage locations
- Compression - reduces the amount of storage space files take up
- Anti-Virus/Malware - protects the computer against threats
- Backup - copies data to another storage device
- Encryption - scrambles data so it cannot be understood

Question 4

Describe open-source software

Answer 4

Source code is freely available for others to amend / recompile

• Can be built on to tailor the program to specific needs without starting from scratch
• Code open for bugs to be spotted and fixed.
• Has the benefit of a community potentially improving the system

Question 5

Describe closed-source software (proprietary)

Answer 5

The source code is not made available

• Distributed in binary form
• There is no permission to amend the program code, so cannot be ‘tweaked’
• Users are sold a license to use it (with conditions).

Question 6

Describe and give examples of software libraries

Answer 6

Pre-written blocks of code that contain useful routines that can be imported into a program.

• Examples: encryption and graphic routines

Question 7

What are the benefits of software libraries?

Answer 7

• Relatively error-free as has already been tested by the author
• Already written so saves development time
• The programmer can use code beyond their expertise
• Often optimised for performance
• Different source languages can be used to increase features

Question 8

What are the negatives of using software libraries?

Answer 8

• May significantly increase the size of the compiled file as the library contains many routines that aren’t being used.
• Not written by the programmer so need to spend time familiarising themselves with it.

Question 9

Describe machine code

Answer 9

• The output of a translator
• Uses binary notation (0101010101000011)
• Dependent on architecture
• Harder to program

Question 10

Describe and give examples of high-level languages

Answer 10

Examples: C# and C++

• Not locked to any architecture (but needs a translator for the given architecture)
• Uses English-like syntax/words.
• Allow for faster development as contains built-in functions to write code quicker.
• Programmer is not in control of what machine code instructions are generated by the translator

Question 11

Describe and give examples of low-level languages

Answer 11

Examples: Assembly and Machine Code

• Machine Code - Written in binary / 1s and 0s.
• Assembly - Uses mnemonics to represent machine code instructions/opcodes
• Assembly - Uses an assembler to convert to machine code
• Assembly - One-to-one conversion to machine code
• Both - Consists of simple instructions
• Both - Processor specific
• Both - Programmer has direct control over what instructions are being run and what memory is being used.

Question 12

What is a translator?

Answer 12

Software that converts code from high-level, or assembly, to machine code

Question 13

What are the 3 types of translators?

Answer 13

• Interpreter
• Compiler
• Assembler

Question 14

Describe an interpreter and give an example of a language that would use one.

Answer 14

• Translates source code every time the program is run
• The user needs access to the source code to run the program
• Will run on any machine
• The slowest option for translators

Example: JavaScript

Question 15

Describe a compiler and give an example of a language that would use one.

Answer 15

• Machine dependent - different compilers are needed for each type of machine
• Creates an executable program (.exe)
• Users do not see the source code
• Only need to be transalted once so saves time when the program is ran
• Code is optimised

Example: C#

Question 16

Describe an assembler and give an example of a language that would use one.

Answer 16

• Used to convert assembly language into machine code
• Replaces mnemonic opcodes with machine codes
• Replaces symbolic addresses with numeric addresses
• Creates one line of object code for each line of source code.

Example: Assembly Language

Question 17

State the stages of compilation

Answer 17

• Lexical Analysis
• Syntax Analysis
• Code Generation
• Optimisation

Question 18

Describe the lexical analysis stage

Answer 18

• Comments and whitespace are removed
• The symbol table is started
• Variable names like ‘count’ are added to a symbol table.
• Reserved words like ‘WHILE’ are tokenized.
• The series of tokens and symbol table is passed onto the next stage, syntax analysis

Question 19

Describe the syntax analysis stage

Answer 19

• Receives output from the lexical analysis
• Code is checked to ensure it follows the rules of the language
• Uses abstract syntax trees to check syntax rules are followed.
• The symbol table is completed
• An error list is generated at the end of this stage

Question 20

Describe the code generation stage

Answer 20

• Receives the abstract syntax trees from syntax analysis
• The object code is created (machine code)
• Turns the code into a format that the processor can understand

Question 21

Describe the purpose of code optimisation along with its pros and cons

Answer 21

The code from the prior stages may have been inefficient (instructions used that can be replaced by simpler ones.)

(+) Ensures the code runs quicker and uses less memory.
(-) Can have unexpected consequences if the code is optimised incorrectly

Question 22

Describe the purpose and types of linker

Answer 22

Used at the end of compilation to combine the object code with the library code to make the single executable file. (Links the main program to libraries)

STATIC - Include full library in the final executable code
DYNAMIC - Points to the external libraries (adds a shortcut to it)

Question 23

Describe the purpose of a loader

Answer 23

• A program in an operating system (OS) used to load the executable file (exe) into memory from secondary storage.
• Loads the required software libraries
• Allocates the memory space to the executable module in main memory.