Spiral Model, advantages and disadvantages of the spiral model in software engineering

In this tutorial we will try to get the answer to the following questions;

1. What is spiral software model?
2. What are phases of the spiral model?
3. When to use spiral model?
4. What are advantages and disadvantages of the spiral model?

What is a spiral model?

The spiral model is a combination of waterfall, incremental, iterative and prototype model. It is mostly used for big projects where continuous changes are required.

Phases of spiral model:

1. Planning
2. Risk analysis
3. Engineering and Construction
4. Evaluation

Phase	Activities	Deliverable
Planning	≡ Requirement gathering ≡ Requirement analysis ≡ Requirement specification ≡ Requirement negotiation ≡ Requirement modeling ≡ Requirement Management	Software Requirement Specification document (SRS)
Risk Analysis	≡ Risk identification ≡ Prioritization of risk ≡ Risk reduction (Mitigation) ≡ Risk impact reduction ≡ Risk monitoring	Risk detailed document
Engineering	≡ Development ≡ Testing	≡ Code ≡ Test cases document, Test report document ≡ Fault report document
Evaluation	≡ Initial Validation by stakeholders ≡ Final Validation by customer	Evaluation report document

 

What are advantages of the spiral model?

≡ Ensure risk reduction

≡ Useful for large projects

≡ Changes can be handled in next iteration/loop.

≡ Most suitable for real-time systems

What are disadvantages of the spiral model?

≡ Expert required for risk reduction

≡ More costly

≡ Not suitable for small projects

≡ Project duration can be infinite because of its spiral behavior.

≡ Project cost can be infinite because of its spiral behavior

≡ Documentation can be very large

≡ Not suitable for the projects with low risk

When to use spiral model?

≡ When risk is medium or high

≡ When software is to be used in very sensitive and dangerous environment.

≡ For real-time systems

≡ For large projects

≡ When requirements are not clear

≡ When changes in the software can be expected at any time.