What is Spiral Model?
The spiral model is a software process model that couples the iterative nature of prototyping with the controlled and systematic aspects of the linear sequential model. Barry Boehm mentioned the Spiral model in this paper (1986).
The spiral model is also known as meta-model since it encompasses all other life cycle models.
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The diagrammatic representation of this model appears like a spiral with many loops, as shown in Figure 4. The exact number of loops in the spiral model is not fixed.
Each loop of the spiral model represents a phase of the software process.
For example, the innermost loop might be concerned with the feasibility study. The next loop with requirements specification, the next loop with design, and so on. Each phase in this model is split into three to six tracks (or quadrants). Figure 4 depicts a spiral model that contains four tracks.
Spiral Model Quadrant (Phases)
The following activities are carried out during each phase of a spiral model.
- First Quadrant (Objective Setting)
– Identify the objectives of the phase.
– Examine the risks associated with these objectives.
- Second Quadrant (Risk Assessment and Reduction)
– A detailed analysis is carried out for each identified project risk.
– Steps are taken to reduce the risks.
- Third Quadrant (Development and Validation)
– Develop and validate the next level of the product after resolving the identified risks.
- Fourth Quadrant (Review and Planning)
– Review the results achieved so far with the customer and plan the next iteration.
– Progressively more complete version of the software gets built with each iteration around the spiral.
When to use Spiral Model
- The spiral model is suitable for the development of technically challenging software products that are prone to several kinds of risks.
- When there is complexity in requirements and need frequent evaluation.
Advantages of Spiral Model
- Suitable for large projects: It is suggested to use the spiral model for large and complex projects.
- Rish handling capability: Project which is complex and large are prone to unknown risk and error. So the spiral model is suitable under these high-risk environments.
- New requirement: Based on the feedback, the requirements are redefined.
Disadvantages of Spiral Model
- Complex: It is one of the most complex SDLC models.
- Documentation: is more as it has many loop iteration.
- Expensive: It is not suitable for small projects.
- Management: is more complex.
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