CSC/ECE 517 Fall 2012/ch2a 2w3 sm

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The Spiral Model



The spiral model is a [software development process] that combines the elements of both design and prototyping-in-stages.This model represents a risk-driven approach to software process analysis. Also known as the spiral lifecycle model (or spiral development), it is a systems development method (SDM) used in information technology (IT). This model incorporates many of the strengths of other models and resolves many of their difficulties. It combines the advantages of top-down and bottom-up concepts and promotes quality assurance through prototyping at each stage.Thus it includes the features of both prototyping and the waterfall model but provides emphasis in a key area which is mostly neglected by other methodologies: deliberate iterative risk analysis. Generally,the spiral model is intended for large, expensive and complicated projects.This approach incorporates elements of specification-driven, prototype-driven process methods, together with the classic software life cycle.[1]


The spiral model was defined by Barry Boehm in his 1986 article "A Spiral Model of Software Development and Enhancement".[2] This model was not the first model to discuss iterative development but it was the first model to explain why the iteration matters. It was created primarily to offer an alternative to the document-driven and code-driven development models, such as the waterfall model, which were being found to be far too prescriptive and unable to handle the inherent risk in software development.
Each phase is characterized by setting a design goal initially and ends with the client (who may be internal) reviewing the progress thus far. Analysis and engineering efforts are applied at each phase of the project, all the way till the end goal of the project is achieved. The key characteristic of a Spiral model is risk management at regular stages in the development cycle


Spiral model is also called as “meta-model”, The name comes from the way the Spiral Model incorporates other Models in the Software Development Life-Cycle. Both waterfall and prototype models are those that are used most often in it. The Software development progresses systematically over the loops (adhering to waterfall approach) and at the same time prototypes are created and displayed to the user after completion of various phases. This ensures a systematic approach with minimal chances of risks.[3]



The spiral model is commonly known as an evolutionary development process.Commonly used as a lifecycle model for software development, the spiral model is similar to the iterative design process as there are repeated iterations (called cycles) in which successive attempts are made to develop a solution.It does so by representing iterative development cycles as an expanding spiral, with inner cycles denoting early system analysis and prototyping, and outer cycles denoting the classic software life cycle. The radial dimension denotes cumulative development costs, and the angular dimension denotes progress made in accomplishing each development spiral.

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