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Definition: Spiral Model
Spiral Model is a SDLC model used in IT project development. It is a combination of iterative development process model (prototyping model) and sequential linear development model (waterfall model) and is also called a meta-model. This model is generally implemented in high risk projects.
There are four phases in a spiral model. A software project has to pass through each of these phases repeatedly, i.e. in iterations. These iterations are referred to as spirals. The baseline spiral starts in the planning phase, after which there requirement gathering is done followed by the risk assessment. Every successive spiral builds upon the base spiral.
The four phases are:
1) Planning phase:
Requirement gathering is done in planning phase. The requirements include BRS (Business Requirement Specification) and SRS (Software Requirement Specification).
2) Risk Analysis:
In this phase, a process is scanned to understand the risks and the alternate solutions possible. If any risk is found, backup solutions are proposed and implemented generating a prototype at the end.
3) Engineering Phase:
Software development is done in this phase along with the testing at the end of the phase.
4) Evaluation Phase:
In this phase, the end user evaluates the project output till date before the project is passed on to the next spiral. This reduces the risk as well as follows a structured approach.
Spiral Model is considered good for large and mission-critical projects. The success of the project is very much dependent on the risk analysis phase. One important advantage is that in this model, additional functionalities can be added to the project at a later date. If at any stage of the project, one feels that the risk involved is much more than anticipated, the project can be aborted. Spiral Model can be an expensive one to use as risk analysis requires highly specific experts. The heavy documentation required at each stage makes it very complex to manage the project.