Software Development Process Model - Part 2

Incremental development

• Rather than deliver the system as a single delivery, the development and delivery is broken down into increments with each increment delivering part of the required functionality.
• User requirements are prioritised and the highest priority requirements are included in early increments.
• Once the development of an increment is started, the requirements are frozen though requirements for later increments can continue to evolve.

Incremental Model

• Deliver the core product first
• Add on / refine features
• Provide a platform for evaluation by user

Incremental development advantages

• Customer value can be delivered with each increment so system functionality is available earlier
• Early increments act as a prototype to help elicit requirements for later increments
• Lower risk of overall project failure
• The highest priority system services tend to receive the most testing

Spiral Development

• Process is represented as a spiral rather than as a sequence of activities with backtracking
• Each loop in the spiral represents a phase in the process.
• No fixed phases such as specification or design - loops in the spiral are chosen depending on what is required
• Risks are explicitly assessed and resolved throughout the process

Spiral model of the software process

Spiral model sectors

• Objective setting
  • Specific objectives for the phase are identified
• Risk assessment and reduction
  • Risks are assessed and activities put in place to reduce the key risks
• Development and validation
  • A development model for the system is chosen which can be any of the generic models
• Planning
  • The project is reviewed and the next phase of the spiral is planned

RAD Model

• Rapid application development model (RAD)
• Characteristics:
  • Extremely short development cycle
  • Component based construction i.e. develop a small component rather than a system
  • Used for information system applications
• Drawbacks:
  • Need more resource for large projects
  • Need commitment from all parties
  • Not suitable for high performance and when technical risk is high
    

Component Based Development Model

• Suitable for re-usable object oriented classes
• Apply characteristics of spiral model

Unified Process

• Work of Ivar Jacobson Grady Booch and James Rumbaugh
• use case driven
• architecture-centric
• iterative and
• incremental

Iterative Development Produces an Executable

Initial and evolution cycles & Time

Rational Unified Process (RUP)

Risk Profiles

Reduce Scrap/Rework: Use an Iterative Process