---
title: "Spiral model, advantages and disadvantages"
subject: "Software Engineering"
chapter: 1
key: "semester_5/software_engineering:spiral-model"
source: https://www.bctengineer.com/q/semester_5/software_engineering/spiral-model
site: BCT Engineering
---

# Spiral model, advantages and disadvantages

Software Engineering · Chapter 1: Software Process and requirements

- Asked in: 2068 Chaitra, 5 marks
- Video: [Spiral Model in Software Engineering | SDLC](https://www.youtube.com/watch?v=y2CnstDLhXM) — Gate Smashers
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/software_engineering/spiral-model
- Whole chapter: https://www.bctengineer.com/md/semester_5/software_engineering/chapter-1

## Question

Describe Spiral model for software development. What are its advantages and disadvantages?

## Short answer

The spiral model is a risk-driven iterative process where each loop sets objectives, assesses and reduces risks (often via prototypes), develops and validates the product, and plans the next loop. Its advantages include explicit risk management, flexibility, early prototypes, and customer reviews; disadvantages are the need for risk expertise, complexity, high cost, and difficulty in estimation.

## Answer

The **spiral model**, proposed by Barry Boehm (1988), is a **risk-driven, iterative** software process model. The process is shown as a spiral instead of a sequence; each loop of the spiral is one phase of development, and the radius shows the cumulative cost so far.

#### The four sectors of each loop
```text
        Cumulative cost (radius grows outward)
   1. Objective setting   |  2. Risk assessment
   - objectives, limits   |     and reduction
   - alternatives         |  - analyse risks
                          |  - build prototypes
   -----------------------+-------------------------
   4. Planning            |  3. Development and
   - review with client   |     validation
   - plan next loop       |  - choose model, build,
                          |    test, validate
```

1. **Objective setting**: define the objectives of this phase, constraints on the process and product, and alternative approaches. Identify project risks.
2. **Risk assessment and reduction**: analyse each key risk in detail and take steps to reduce it, for example by building a prototype, doing a simulation or a benchmark.
3. **Development and validation**: choose a development model suited to the remaining risk (prototyping, waterfall, formal methods) and develop and validate the next version of the product.
4. **Planning**: review the project with the customer and decide whether to continue with another loop. If so, plan the next phase.

Typical loops move outward from concept of operation, to requirements, to design, to detailed design, code, test and deployment.

#### Advantages
- **Explicit risk management**: high-risk problems are found and handled early.
- Combines the strengths of other models; waterfall and prototyping can be used inside it.
- **Iterative**: requirements can be refined and changes accommodated.
- Customer reviews every loop, so there is good **user feedback**.
- Suitable for **large, complex and high-risk** projects.
- Working versions/prototypes appear early.

#### Disadvantages
- Success depends on **risk-assessment expertise**; poor risk analysis leads to failure.
- **Complex** to manage; more documentation and reviews.
- **Costly**; not suitable for small or low-risk projects.
- Hard to define fixed milestones, so **cost and time are hard to estimate** at the start, which makes fixed-price contracts difficult.
- The spiral may continue for a long time if there is no clear stopping point.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Who proposed the spiral model, and what is its main driver?
   A. Royce; documents
   B. Brooks; team size
   C. Boehm; risk
   D. Pressman; cost only
   Answer: C. The spiral model was proposed by Barry Boehm (1988) and is risk-driven and iterative. (Key point: Nature of spiral model)

2. Which sequence correctly lists the four sectors of a spiral loop?
   A. Coding, testing, deployment, maintenance
   B. Objective setting, risk assessment and reduction, development and validation, planning
   C. Planning, coding, testing, billing
   D. Requirements, design, implementation, maintenance
   Answer: B. Each loop has objective setting, risk assessment and reduction, development and validation, and planning. (Key point: Four sectors)

3. What is done in the risk assessment and reduction sector?
   A. Key risks are analysed and reduced, e.g. by prototypes, simulation or benchmarks
   B. The final product is delivered to users
   C. The customer signs off the whole project
   D. Only documents are written
   Answer: A. Risks are analysed in detail and steps such as prototyping, simulation or benchmarking are taken to reduce them. (Key point: Risk assessment sector)

4. What does the radius of the spiral represent?
   A. Number of developers
   B. Cumulative cost so far
   C. Size of the customer organisation
   D. Remaining risk
   Answer: B. The radius shows the cumulative cost incurred so far in the project. (Key point: Radius of the spiral)

## Related in Software Engineering

- [Software runaways; waterfall and prototyping inside spiral](https://www.bctengineer.com/question.md?key=semester_5%2Fsoftware_engineering%3Asoftware-runaways-spiral) — Software Engineering, chapter 1
- [Why software development is complex; man-month myth](https://www.bctengineer.com/question.md?key=semester_5%2Fsoftware_engineering%3Acomplex-development) — Software Engineering, chapter 1
- [Waterfall versus spiral; user participation](https://www.bctengineer.com/question.md?key=semester_5%2Fsoftware_engineering%3Awaterfall-vs-spiral) — Software Engineering, chapter 1
- [Waterfall model: advantages and limitations](https://www.bctengineer.com/question.md?key=semester_5%2Fsoftware_engineering%3Awaterfall-limitations) — Software Engineering, chapter 1
- [Prototype model and when to use it](https://www.bctengineer.com/question.md?key=semester_5%2Fsoftware_engineering%3Aprototype-model) — Software Engineering, chapter 1
- [Book store process model](https://www.bctengineer.com/question.md?key=semester_5%2Fsoftware_engineering%3Abook-store-process-model) — Software Engineering, chapter 2

## Related in other subjects

- [Spiral model of software development](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Aspiral-model) — Instrumentation II, chapter 9, asked 3×
- [Spiral model of embedded software life cycle](https://www.bctengineer.com/question.md?key=semester_6%2Fembedded_system%3Aspiral-model-esdlc) — Embedded System, chapter 3
- [Prototyping model of software](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Aprototype-model) — Instrumentation II, chapter 9, asked 3×
- [Compare software models; propose a fourth model](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Asw-models-compare-fourth) — Instrumentation II, chapter 9