Spiral Model of Software Development & Validation.
Information & Understanding. | Software Validation.The Spiral Model of software development and validation is a combination of an iterative process model and a linear development model such as the Waterfall Model.
The Spiral Model permits incremental releases or revisions of the software through each iteration around a spiral. A key advantage of the spiral model is that is imposes risk consideration and mitigation in the software development and testing process.
In the spiral model each complete circle is called a loop, and within each loop are four phases (occupying four quadrants). A software project continually progresses through each of these loops in iterations called spirals. The total number of loops will be determined by the project magnitude and complexity.
The four phases are:
1)Determine Objectives, Alternatives & Constraints. In the first phase “determine objectives”, the “baseline spiral” requires that the business requirements for the software project are understood. Following-on in each loop of the spiral as the development process progresses, are identified the system requirements, sub-system requirements, unit requirements, etc..
2)Identify Risks, Evaluate Alternatives and Resolve. In this phase all the potential solutions to address the prior phase objectives are reviewed and assessed, with the objective of identifying the optimum solution. The risks which then may arise as a result of progressing to implement the selected solution are now identified and actions taken to understand and mitigate those risks.
3)Development and Test. In this phase the software product is further developed versus the identified required features and tested. In the first loop, the developed software is effectively a “proof of concept”.
4)Review and Plan for the next iteration. The software project is reviewed and decisions made in determining if a new loop needs to be progresses. Have all requirements been identified and delivered upon? Are all potential risks associated with the requirements understood and addressed?
References: “Spiral Development: Experience, Principles, and Refinements”, Barry Boehm, Carnegie Mellon, Software Engineering Institute.
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