SLR05 - Application generation

Application examples

• Word processor

• Spreadsheet

• Database

• Web browser

• Graphics manipulator

Generic application VS Specific application

• Generic application - (eg. word processor) no narrow process and can be used for general or specific task, more commonly installed

• Specific application - (eg. database software) highly specific & essential for creating serious database applications

Utility software

• Program with one purpose

• Used to maintain the system

Types of utility software

• Defragmentation

• Anti-malware

• Data compression

• Backup

• File repair

Defragmentation

• Reorganises file on hard drive, put fragments of files & empty space together = reduce read/write head across surface disk = speeds up file access

• Solid state no defragmented, no moving parts

Anti-malware

• Help keep computer & files safe from malware

Data compression

• Compression decrease size file = faster download

• Compressed file must be extracted before read

Backup

• Can schedule backups

• Full/increment backups

• Can backup to of site cloud

• Can come with OS or purchased separately

File repair

• File can corrupt

• File repair software attempts correct issue & restore file

• Can be built into some software or separate

Open source software

• Not protected by the Copyright Design & Patents act

• User access source code

• Can modify & distributed

• Can be installed any number of computers

• Support by community

• May not be fully tested & quality varied

Open source software Benefits & Drawbacks

• Software free

• Wide community modifications

• Creator gets software out there to wider community

• Possibly poor supported

• Some features not tested

• Little to no financial gain

Closed source software

• Protected by Copyright Design and Patents Act

• User cannot modify software

• Usually paid per licence

• Supported by devs - not release source code

• Tested by devs prior to release, may run beta

Closed source software Benefits & Drawbacks

• Well supported, tested, professionally built products

• Creator receives income

• Cost or ongoing subscription

• Constant demand from community for more featured & improvements

• Piracy issues

Assembler

• Translates assembly language to machine code

• Usually one-to-one process from assembly code to machine code

Assembley benefits & drawbacks

• Program written in machine language can be replaced with mnemonics - easier to remember

• Memory efficient

• Faster speed of execution

• Hardware oriented

• Takes long time to code

• Difficult to remember syntax

• Long programs cannot be executed on small computers

• Lack of portability between different computers

Compiler

• Translate source code from high level language to object code to machine code

• Whole program translated to machine code before run

Compiler benefits & drawbacks

• No need for translation run time

• Executes faster

• Code optimised

• Source code kept secrete

• Program not run with syntax errors = difficult

• Code need recompiled when changed

• Designed for specific processor

Interpreter 

• Translates high level to machine code

• Translates line by line

Interpreter benefits & drawbacks

• Stop at syntax error - easier

• Not recompiled when changed

• Translation software required

• Speed slower

• Code not optimised

• Source code required

What are the 4 stages of compilation?

1. Lexical analysis

2. Syntax analysis

3. Code generation

4. Code optimisation

Lexical Analysis

• Comments and white space removed

• Lexemes are identified and converted to tokens with token classes eg. [keyword:WHILE]

• Symbol table created to keep track of tokens such as variables & subroutines

Syntax Analysis

• Checks syntax of code using language’s rules

• Errors generated if any tokens break rule

• Produces abstract syntax tree using tokens from previous stage - tree outlining the syntax the code must follow

Code generation

Abstract syntax tree converted to object code - the machine code generated before the final step (linker) is run

Optimisation

• Reduces execution time of the program

• Spots redundant instruction & producing object code that achieves the same effect as source program

• Removing subroutines, variables, constants that are never referenced

Libraries

• Complied & tested programs that can be run when needed

• Typically grouped into software libraries

Benefits of libraires

• Save time & effort as it can be easily implemented

• Pre-tested = error free

• Pre-compiled & optimised

• Same library can be used in different parts of a project or in different projects

Drawbacks of libraires

• Adding & tweaking difficult

• Don’t know how efficient library is

• Need to trust devs to maintain library

• Compatibility issues between code & library or multiple libraries

Linkers

• Combine different code files and libraries into a single executable

• Resolve references between files, ensuring everything points where it should

Static Linking

• Libraries are combined with the code at compile time

• Creating a larger executable

Dynamic linking

• Libraries are linked at runtime

• Allowing for more flexibility

• But requiring the library to be present during execution

Loader

system tools that load executable files into memory so they can be run by the operating system