Software Engineering Spiral Model

Spiral Model

In 1986, the Spiral model was proposed by Barry Boehm.
The Spiral model is an evolutionary approach combining iterative development with systematic risk analysis.
It is particularly suitable for large, complex and high-risk projects.
Development proceeds through repeated cycles (spirals); each loop represents an iteration.
Each loop may contain planning, risk analysis, engineering and evaluation activities.
The model supports continuous refinement until the system meets stakeholder needs.

The core activities in each spiral are:

Collect requirements and perform feasibility studies. Define objectives, schedule, resources and success criteria for the upcoming iteration.

Identify potential risks (technical, cost, schedule) and evaluate options to mitigate them. Select the best approach and plan contingencies.

Develop prototypes or system increments and test them. Because iterations are frequent, testing is integrated into each cycle.

Obtain stakeholder feedback, review outcomes and decide whether to proceed to the next spiral or adjust plans based on findings.

Well-suited for large, high-risk projects where risk management is essential.
Early and repeated customer feedback reduces the chance of delivering the wrong system.
Risks are addressed early through analysis and prototyping.
Flexible — requirements can evolve between iterations.
Produces well-documented and incremental deliverables aiding maintenance.

Not economical for small or low-risk projects due to overhead of repeated risk analysis.
Can be complex to manage and difficult for newcomers to grasp.
May be more expensive and time-consuming compared to simpler models.
If not controlled, iterations could continue indefinitely without clear endpoints.
Requires strong risk-assessment skills and stakeholder commitment.