Spiral Model in Software Engineering

Spiral Model

• It is flexible and can deal with changes easily
• It involves user involvement, which improves user satisfaction
• New ideas and functionality can be added at a later stage
• It is applicable for large problem only
• It can be more costly to use
• It is more complex to understand
• More documents are needed as more spirals are added

Spiral Model Quadrants

• 1st Quadrant: Determine Objectives
• 2nd Quadrant: Identify and resolve risks
• 3rd Quadrant: Develop next level product
• 4th Quadrant: Review and planning

Spiral Model Graph

• Radius represents cost
• Angular dimension represents progress of the current phase

Prototype Model

• A working physical system or subsystem
• A partial developed product
• Limited functional capabilities
• Low reliability
• Inefficient performance
• Useful in developing GUI part of system
• Quick design and build prototype
• Submit to customer for evaluation
• Refine requirements and modify prototype
• Repeat until customer approval
• Then, develop actual system using iterative waterfall model

Prototype Model Advantages

• Partial product is built initially, allowing customer preview
• New requirements can be accommodated easily
• Quicker user feedback for better solution
• Chance of user satisfaction is higher

Prototype Model Disadvantages

• Code is usually thrown away, wasting time
• High construction cost
• Losing customer interest if initial prototype is unsatisfactory

Prototype Model When to Use

• When system needs interactions with end-users
• Generally used in GUI type of development

Agile Model

• Based on iterative development
• Break tasks into smaller iterations
• No long-term planning
• Project scope and requirements laid down at the beginning
• System broken down into modules, implemented and delivered incrementally
• Core product developed first
• Core product used by customers to evaluate
• Initial product skeleton refined into increasing levels of capability

Incremental Model

• Each successive version performs more useful work
• Core modules get thoroughly tested, reducing error chance
• Model is flexible and less costly to change scope and requirements
• User gets to experiment with partially developed software
• Feedback at each increment helps determine better final product

Incremental Model Disadvantages

• Difficulty in subdividing problems into functional units
• Model can be used for very large problems
• Needs good planning and design

Incremental Model When to Use

• When problem is very large and user requirements are not well specified initially

RAD Model

• Proposed by IBM in 1980
• Emphasizes extremely short development cycle
• Emphasizes reuse
• User involvement essential from requirement analysis to delivery
• Requirements must be cleared and well understood initially
• Can create a fully functional system within short time periods