1. Incremental Waterfall
The Spiral Model
Incremental Waterfall
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2. Introduction
This was first introduced to combine the best features of the waterfall and interation from the prototyping models
It also emphasizes risk analysis
It dates from a paper by Boehm in 1986
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3. Four Phases Identification Design Build Risk Analysis
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4. Diagram
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5. Identification Starts with gathering the business requirements
In subsequent iterations there is the identification of system requirements, subsystem requirements and unit requirements
Each spiral requires communication between the user and developers
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6. Design Starts with the conceptual design in the first iteration
Subsequent spirals involve architectural design, logical design of modules, physical product design and final design
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7. Construct or Build
Refers to production of the actual software product at every spiral.
In first spiral the design is being developed as a proof of concept to get customer feedback.
In the subsequent spirals requirements and design details are refined
A working model of the software is produced
These are sent for customer feedback
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8. Evaluation and Risk Analysis
This includes identifying, estimating, and monitoring technical feasibility and management risks
Including schedule slippage and cost overrun
After testing the software the user evaluates and gives feedback
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9. Reasons to Use Budget constraints and risk evaluations are important
Medium to high-risk projects
User is unsure of requirements
Requirements are complex and/or not well understood
Product lines will be released in phases to get customer feedback
Significant changes are expected in the product during the development cycle
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10. Pros Changing requirements can be accommodated
Allows for extensive use of prototypes
Requirements can be captured more accurately
Users see the system early
Development can be divided into smaller parts and more risky parts can be developed earlier
This aids risk management
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11. Cons Management is more complex. End of project may not be known early
Not suitable for small or low risk projects and could be expensive for small projects
Process is complex
Spiral may go on indefinitely
Large number of intermediate stages requires much documentation
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12. Finally Has some of the aspects of waterfall and prototyping
Much greater risk consideration
Has much of the flavor of several agile methods
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