Spiral model appears as a spiral having the loop.
The number of loops the product development will require totally depends on the requirement. Thus it varies from project to project.
Each loop in the spiral model is a phase.
Here we can have any number of loops depending upon our requirement. It means the project can be worked in phases.
This model is much flexible in comparision to other model that we studied so far as the number of phases through which product is developed is not fixed and defined.
In each loop some features are analyzed to filter out the risks involved in developing it and is resolved immediately through prototyping. Once it is done the features analyzed during the loop is implemented or developed.
Phases of Spiral model
Phases of the spiral model is:
Determine objectives and identify alternative solutions
Identify and resolve risks for each solution identified
Develop next level of the project
Review and plan for the next phase
Phases of spiral model is represented graphically in the following diagram:
Spiral model is preferred for projects that might have chances of showing up many unknown risks as development work progress.
Spiral model as Meta model
Spiral model can be seen as meta model as it incorporates all the discussed models so far.
A single loop represents the waterfall model and its systematic step-wise approach.
The spiral loop uses the protyping model as well to identify and reduce risk before the actual development work starts
As the loop is not fixed, so each loop can be considered as evolutionary level of development.
Shortcomings of Spiral Model
Spiral model appears to be a complex and complicated model.
This model requires knowledgeable staff.