Software Development Methodologies

• A software development methodology which focuses on the early delivery to end users of an incomplete, but working, system which can be changed following feedback from the client.
• A prototype enables the end users to evaluate the proposals for the design of software by trying them rather than having to interpret and evaluate the design based on descriptions.
• End user can find it difficult to define their exact requirements.
• Prototyping is used to check that what the end users want and need.
• A prototype enables design options to be tried out and problems with possible solution to be investigated.
• There are 2 types of prototyping:
  • Evolutionary
  • Throw - away

• An initial prototype is developed and evaluated by the end users
• Using this feedback a second prototype is developed and evaluated.
• This process continues with each prototype and evaluation making the system closer to what the end users required.
• On the last evaluation, the system should meet all the requirements.

• A working model of various parts of the system is developed after a short investigation.
• The prototype is developed and evaluated by the end users but is not used in the final solution - it is thrown away.
• This allows the end users to give, and recieve quick feedback, which means that any refinements can be done early in the development.
• This is cost effective as there is nothing to redo.
• If a project is changed after considerable work has been done, then small changes could require large efforts to implement since software systems have many dependencies.

• Advantages of prototyping include:
  • Reduced time and costs
  • Improved and increased user development
  • Earlier feedback from the end user canbe obtained by the desiger
  • The avoidance of the expense and difficulty of changing a finished software product
• Disadvantages of prototyping include:
  • End user confusion between the prototype and finished system
  • Excessive development time of the prototype

NOTE : This methodology cannot be used where user requirements are well established or the system is a standard one used by the organisation.

• A software development methodolgy based on a system life cycle that is iterative and evolutionary.
• The aim of RAD is to produce a software solution in less than 6 months (considered to be the longest time scale over which user requirements will stay static).
• RAD has 2 features:
  • The use of joint application design (JAD workshop)
    • Aim to develop a set of requirements that should not change before the system is implemented.
  • Use of timeboxing
    • The requirements of the system are defined in small chunks each of which is considered using a JAD.
    • 

• Advantages of RAD include:
  • End users are involved at all stages with the system being implemented within 6 months.
  • End users are involed in the evaluations so this should ensure that the final system fully meets their defined requirements.
  • End users don't have to refine all the requirements of the system at the beginning of the process.
• Disadvantages of RAD include:
  • The solution developed using RAP may, on the surface, meet the end user requirements but the funtionality may not be acceptable.
  • The project manager, who is overseeing the development of the system, will need to keep a very tight control over the whole development process and the  team, if the system is to be developed within 6 months deadline required by RAD.

NOTE : This methodology should not be used where the user requirements include safety critical components.