1.2.2 Applications Generation

Question 1

What are the two types of software?

Answer 1

Applications and systems

Question 2

What is an application?

Answer 2

A program that can be run on a computer, allowing the user to carry out specific tasks.

Question 3

Give examples of applications software

Answer 3

Word processing, spreadsheets, web browsers.

Question 4

Give examples of systems software.

Answer 4

Library programs, utility programs, operating system, drivers

Question 5

What are utilities?

Answer 5

System software with a specific purpose, usually related to maintenance.
(EG: Optimising computer performance, backing up files)

Question 6

Provide examples of utilities

Answer 6

Compression, Disk defragmentation, antivirus, automatic updating, backup

Question 7

Disk defragmentation

Answer 7

Rearranges contents of the hard drive so they can be accessed faster, thus improving performance.

Question 8

Define open source software

Answer 8

• Can be used by anyone without a license
• Distributed with the source code.

Question 9

Define closed source

Answer 9

Requires the user to hold an appropriate license to use it. Source code cannot be accessed as the company owns the copyright license.

Question 10

Pros: Open source

Answer 10

Pros
- Can be modified and improved by anyone
- Technical support from online community
- Can be modified and sold on

Question 11

Pros: Closed Source

Answer 11

Pros
- Thorough, regular and well tested updates.
- Company owning software provides expert support and user manuals.
- High levels of security as developed professionally.

Question 12

Cons: Open source

Answer 12

Cons
- Support available online may be insufficient or incorrect. No user manuals.
- Lower security, as it may have not been developed in a controlled environment.

Question 13

Cons: Closed source

Answer 13

Cons
- License restricts how many people can use the software at once.
- Users cannot modify and improve software themselves

Question 14

What three things must user consider when deciding between open source or closed source?

Answer 14

• Relevance to task
• Costs (implementation, maintenance, license)
• Functionality (ease of use, features available)

Question 15

What is a translator?

Answer 15

A program that converts high level source code into low level object code.

Question 16

What are the three types of translator?

Answer 16

Compiler, Interpreter, Assembler

Question 17

What does a Compiler do?

Answer 17

Compilers translate high level code into machine code all at once, after carrying out a number of checks and reporting back any errors.

Question 18

What is compiled code specific to?

Answer 18

A particular processor type and operating system.

Question 19

Compiler Disadvantages

Answer 19

• The initial compilation process is longer than using an interpreter or an assembler
• If changes need to be made, the whole program must be recompiled.
• Once code has been compiled, it can only be executed on certain devices.

Question 20

Compiler Advantages

Answer 20

• Once code has been compiled, it can be run without a translator being present

Question 21

Interpreter

Answer 21

Interpreters translate and execute code line-by-line. They stop and produce an error if a line contains an error.

Question 22

Interpreter Disadvantages

Answer 22

• Code must be translated each time it is executed.
• Interpreted code requires an interpreter in order to run on different devices.

Question 23

Interpreter Advantages

Answer 23

• Useful for testing sections of code and pinpointing errors
• Interpreted code is more portable. As long as the right interpreter is available, code can be executed on a range of platforms

Question 24

What do assemblers do?

Answer 24

Translate assembly code into machine code. Code is translated on almost a one-to-one basis.

Question 25

What are the four stages of compilation?

Answer 25

Lexical analysis, Syntax analysis, code generation and optimisation.

Question 26

Syntax Analysis

Answer 26

1) Tokens are checked against the grammar and rules of the programming language. Any tokens that break the rules are flagged up as syntax errors, and added to a list of errors. 2) An abstract syntax tree is produced, which represents the source code in the form of a tree. 3) Semantic analysis is carried out, where logic mistakes within the program are detected.

Question 27

What are examples of syntax errors?

Answer 27

Incomplete set of brackets, undeclared variable type

Question 28

What are examples of semantic errors?

Answer 28

Multiple declaration, undeclared identifiers.

Question 29

Lexical Analysis

Answer 29

1) Whitespace and comments are removed from code. 2) The remaining code is analysed for keywords and names of variables and constants. These are replaced with tokens. 3) Information about the token associated with each keyword or identifier is stored in a symbol table.

Question 30

Code Generation

Answer 30

The abstract syntax tree produced in the syntax analysis stage is used to produce machine code.

Question 31

Optimisation

Answer 31

1) Redundant parts of code are detected and removed. 2) Repeated sections of code may be grouped and replaced with a more efficient piece of code that produces the same result.

Question 32

What is the danger involved with the optimisation stage?

Answer 32

Excessive optimisation may alter the way in which the program behaves.

Question 33

What is a linker?

Answer 33

A piece of software which links external modules and libraries included within the code.

Question 34

What are the two types of linker?

Answer 34

Static and Dynamic

Question 35

Static Linker

Answer 35

Modules and libraries are added directly into the main file, increasing the file size.

Question 36

Dynamic Linker

Answer 36

Addresses of modules and libraries are included in the file where they are referenced. When the program runs, the loader retrieves the program at the specified address so it can be executed.

Question 37

Advantage of dynamic linker

Answer 37

- Files remain small - External updates feed through to the main file, meaning theres no need to rewrite the code.

Question 38

What are loaders provided by? What do they do?

Answer 38

Programs provided by the operating system. When a file is executed, it retrieves the library or subroutine from the given memory location.

Question 39

What are libraries?

Answer 39

Pre-compiled programs which can be incorporated within other programs using either static or dynamic linking.

Question 40

What are advantages of libraries?

Answer 40

- They are ready to use and error free, which saves development time. - They can be reused within multiple programs.

Question 41

What do libraries often provide? Why is this useful?

Answer 41

A specialised range of functions. These functions would require a lot of time and effort to develop, saving programmers from having to 'reinvent the wheel'.

Question 42

What benefit does the optimisation stage provide?

Answer 42

Code is faster to execute.

Question 43

Benefit of using static linker

Answer 43

It allows you to use a specific version of a library, as updates to modules and libraries externally dont affect the program.