Application Development

1
Chapter 10

• Application Development

2
Chapter Goals

• Describe the application development process and
  the role of methodologies, models and tools
• Compare and contrast programming language
  generations
• Explain the function and operation of program
  translation software, including assemblers,
  compilers and interpreters
• Describe link editing and contrast static and
  dynamic linking
• Describe integrated application development
  software, including programmers work-benches and
  CASE tools

3
Software Development

• Process of translating user needs into CPU
  instructions
• This is a complex process that requires
  significant effort and resources
• Software is the most costly component of IS

4
Software Development
5
Systems Development Life Cycle
6
SDLC Phases

• Systems requirement model provides the detail
  needed to develop a specific system to meet user
  needs
• Design model provides an architectural
  blueprint for system implementation

7
Development of programming languages
8
Programming Languages
9
Programming languages

• Language used to instruct a computer to perform a
  task
• Programming language development has tried to
• Make the language easier to understand
• Develop a language that takes less time (requires
  fewer instructions) to complete a task

10
Programming languages cont.

• Variety of programming languages
• Link to Google programming languages page
• http//directory.google.com/Top/Computers/Programm
  ing/Languages/

11
Development of languages

• First Generation binary CPU instructions
• First programmers wrote code as sequences binary
  digits
• Tedious and error prone
• As software grew in complexity this became
  unpractical

12
Languages cont.

• Second generation language assembly languages
  (simple machine)
• Mnemonic represents CPU instruction
• Mnemonic can also represent location in memory
  (variable)
• Mnemonic can also represent a program instruction
  memory address (label)

13
Assembler

• Code from 2GL (Assembly code) is translated into
  binary instructions by Assembler
• Translates each mnemonic into its corresponding
  binary digit sequence
• Programmer still required to write one assembly
  instruction per CPU instruction
• 2GL is for a specific CPU (i.e. processor)

14
Machine independence

• Programs written in 2GL (assembler) only work for
  a specific CPU
• Companies spend a long time developing custom
  systems
• These systems continue to evolve over time
• New modules added
• Systems updated and maintained over time

15
Machine independence cont.

• When company buys a new computer (i.e. new CPU)
  what happens to the old software?
• Still a problem, still a lot of mainframe systems
  running (COBOL) due to difficulty of porting to a
  new computer

16
3G languages

• 3GLs address the issue of machine independence
• Code is standardized (ANSI, etc.)
• Special software called a compiler takes standard
  code and translates it to a specific CPU
• Each CPU needs to have its own version of the
  compiler

17
3GLs

• FORTRAN, COBOL, BASIC,PL/1, Pascal and C
• 3GL code is translated (compiled) into assembly
  code, then into binary code
• First languages to exploit machine independence
  3GL code is the same regardless of the CPU that
  executes it

18
Languages cont.

• Third generation language allows programmers to
  specify many CPU instructions per program
  instruction or statement
• This one-to-many (1N) relationship is called
  instruction explosion

19
Instruction explosion

• One line of code Cobol, Pascal, C are
  translated into many lines of CPU instructions
• Makes programmer more productive
• CPU code is more efficient
• Compiler (software that generates CPU
  instructions) can optimize CPU instructions

20
4GLs

• Addressed the following limitations of 3GL
• Higher instruction explosion
• Ability to develop GUI
• Ability to interact with database
• Most 4GL were proprietary packages
• VB and SQL are still in use

21
Object Oriented Languages

• OOP is an attempt to address problems of software
  maintenance and re-use
• Data and programs are viewed as integrated parts
  called objects
• Objects communicate using methods
• Client server model
• Prominent examples C, Java

22
OOP systems models
23
Language standardization

• American National Standards Institute (ANSI) and
  International Standards Organization (ISO) set
  standards for programming languages (C, C,
  COBOL)
• Advantage guarantee portability between
  platforms, promotes machine independence
• Disadvantage slow to improve and develop

24
Creating executable code

• Modern programming languages use a syntax more
  suited to human understanding
• Computer requires instructions made out of 0s and
  1s

25
Creating .exes cont.

• Software applications have become quite complex
• Hundreds if not thousands of programmers
  contribute part of the solution
• Solutions are designed to be re-usable

26
Producing an .exe

• Individual programmers work needs to be
  translated into machine code
• Translate the source code of an individual file
  into 0s and 1s
• All the work of many programmers needs to be
  packaged together
• Collect and bundle different parts of binary code
  into a single load module

27
IDE

• Integrated development environment is a software
  development tool that brings together software
  tools to facilitate
• Translating higher order languages into 0s and 1s
  (binary code)
• Managing and combining libraries of existing
  programming solutions

28
Compiler
29
Steps in development process

• Programmer produces a program in a specific
  language
• Program is called source code
• Code is made up of
• Data declarations
• Statements
• Function calls (using pre-written library
  routines)

30
Steps cont.

• Source code (as produced by programmer) becomes
  input into compiler
• Compiler tests each line of code comparing it to
  syntax requirements of specific language
• If errors exist, produces an error report
• After clean compile compiler produces object
  code (assembly instructions)

31
Output of compile step

• Symbol table list of variable names associated
  with a memory location
• Assembler instructions mnemonic for CPU
  instructions

32
Symbol table
33
Steps cont.

• Object file (output of compile step) becomes
  input into next step link editor
• Link editor combines object file with code from
  software libraries
• Output of link step is .exe file

34
Example in C

• Example program showing compile link and exe
  output
• Go to Visual C

35
Link Editor

• Modern programming languages allow programmers to
  use pre-existing routines in their code
• Using a function is referred to as a function
  call
• A link editor searches object code (the output of
  the compile step) for references to external
  library function calls
• When an external function call is found, the link
  editor searches for the corresponding executable
  code that implements the function

36
Link editor
37
Benefits of a link editor

• Allows a project to be developed among different
  files (i.e. each programmer develops a separate
  file)
• A single executable program can be constructed
  from multiple object code files compiled at
  different times
• A single compiler can generate executable
  programs that run under multiple operating
  systems

38
Dynamic vs. static binding

• Dynamic Linking linking is performed during
  program loading or executionexample DLLs and
  Visual Basic, Java
• Static Linking library and other subroutines
  cannot be changed once they are inserted into the
  executable codeexample C program

39
Dynamic vs. static linking

• Dynamic Linking Advantages
• Smaller application program files
• Flexibility
• Static Linking Advantages
• Execution speed
• Improved reliability and predictability of
  executable programs

40
Interpreters

• Reads a single source code instruction,
  translates it into CPU instructions or a DLL call
• Advantage flexibility to incorporate new or
  updated code into an application program
• Disadvantage increased memory and CPU
  requirements during program execution

41
Visual Basic

• Is an interpreted language
• See VB example

42
Compilers vs. Interpreters
43
Java language

• OOL developed by Sun
• Originated as operating system for interactive
  TVs
• Applied to demands of producing code for a
  distributed computing environment (i.e. the Web)

44
Java web resources

• Java web site http//java.sun.com/
• Java software http//java.sun.com/java2/
• Java documentation http//developer.java.sun.com/d
  eveloper/infodocs/?frontpage-main
• Java tutorials http//java.sun.com/docs/books/tuto
  rial/
• Java applet examples http//javaboutique.internet.
  com/javasource.html

45
Development for the Web

• What are the requirements for an application
  development tool designed to produce applications
  for a distributed computing environment?

46
Requirements

• Seamless multi-platform capability
• Built in security protection capabilities
• Multi-threaded, i.e. easily break a problem into
  independent sections run concurrently
• How does Java address these requirements?

47
Java Requirements

• Multi-platform
• Java virtual machine
• Built in security
• Security restrictions for applets
• Multi-threaded
• Built-in thread class in standard library

48
Java
49
Java example

• Run java example with java console

50
Microsofts Answer

• .Net framework
• Supports 20 different programming languages
• Supports distributed networked applications (see
  presentation)

51
Summary

• Application systems are developed by following
  the steps of the systems development life cycle.
  (SDLC)
• Executable software consists entirely of CPU
  instructions
• All programming language generations other than
  the first must be translated into CPU
  instructions prior to execution
• Compiled and interpreted programs must be linked
  to libraries of executable functions or methods
• Application development is more efficiently
  supposed by integrated suites of automated tools