---
title: "Compare software models; propose a fourth model"
subject: "Instrumentation II"
chapter: 9
key: "semester_5/instrumentation_ii:sw-models-compare-fourth"
source: https://www.bctengineer.com/q/semester_5/instrumentation_ii/sw-models-compare-fourth
site: BCT Engineering
---

# Compare software models; propose a fourth model

Instrumentation II · Chapter 9: Software For Instrumentation And Control Applications

- Asked in: 2071 Chaitra, 4 marks
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/instrumentation_ii/sw-models-compare-fourth
- Whole chapter: https://www.bctengineer.com/md/semester_5/instrumentation_ii/chapter-9

## Question

Compare and contrast the three traditional models of software development with respect to their strengths and weaknesses. Propose a fourth software development model that outperforms the classical methods and justify your choice in terms of reliability, maintainability, flexibility, portability and reusability.

## Short answer

Waterfall is rigid, prototyping causes scope creep, spiral is complex. A hybrid iterative-incremental model with risk-driven prototyping improves reliability through early testing, maintainability by modular increments, flexibility via feedback, portability by isolating hardware, and reusability of components.

## Answer

#### Comparison of the three traditional models
| Model | Strengths | Weaknesses |
|---|---|---|
| Waterfall | Simple, clear phases, good documentation, easy to manage | Rigid, late working product, poor change handling |
| Prototyping | Early user feedback, clarifies requirements, high satisfaction | Poor structure and documentation, scope creep, extra cost |
| Spiral | Risk-driven, flexible, iterative for large projects | Complex, costly, needs risk expertise |

#### Proposed fourth model: Iterative-incremental with risk-driven prototyping (hybrid, agile-like)
The product is divided into increments. For each increment: quick requirements, risk analysis, prototype of risky parts, design, coding, testing (with automated tests) and delivery to the customer for feedback. Stable core is planned like waterfall; changes are handled in later increments.

```text
 Core plan -> [Increment 1: req-design-code-test] -> release
           -> [Increment 2: ...] -> release ... -> final
```

#### Justification
- **Reliability:** testing and risk analysis happen in every increment; bugs are found early.
- **Maintainability:** modular increments, continuous documentation and version control.
- **Flexibility:** feedback after each release allows requirement changes.
- **Portability:** hardware-dependent parts isolated in separate modules.
- **Reusability:** tested components and libraries from earlier increments are reused.

## Check yourself

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

1. Strength of Waterfall?
   A. Early user feedback
   B. Risk-driven iteration
   C. Handles change well
   D. Simple, clear phases and good documentation
   Answer: D. Waterfall is simple and well documented. (Key point: Waterfall)

2. Weakness of Spiral?
   A. Complex, costly and needs risk expertise
   B. Poor risk handling
   C. Late documentation
   D. Too simple
   Answer: A. Spiral is costly. (Key point: Spiral)

3. The proposed fourth model is what?
   A. Pure waterfall
   B. Iterative-incremental with risk-driven prototyping
   C. Big-bang release
   D. Code-and-fix
   Answer: B. It delivers in increments with risk analysis. (Key point: Proposed model)

4. How does it support reusability?
   A. Code is discarded each time
   B. Nothing is documented
   C. Tested components from earlier increments are reused
   D. Only hardware reused
   Answer: C. Earlier tested components and libraries are reused. (Key point: Reusability)

## Related in Instrumentation II

- [Shortcomings of software development models](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Asw-model-shortcomings) — Instrumentation II, chapter 9
- [Spiral model of software development](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Aspiral-model) — Instrumentation II, chapter 9, asked 3×
- [Software reliability; waterfall vs prototyping; embedded software](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Asw-reliability-models-embedded) — Instrumentation II, chapter 9
- [Software process models and effort estimation](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Asw-process-models) — Instrumentation II, chapter 9, asked 2×
- [Prototyping model of software](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Aprototype-model) — Instrumentation II, chapter 9, asked 3×
- [Increasing reliability of embedded real-time software](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Aembedded-rt-reliability) — Instrumentation II, chapter 9

## Related in other subjects

- [Software reliability and reliability models](https://www.bctengineer.com/question.md?key=semester_5%2Fsoftware_engineering%3Areliability-models) — Software Engineering, chapter 9, asked 2×
- [K-means strengths and weaknesses](https://www.bctengineer.com/question.md?key=semester_7%2Fdata_mining%3Akmeans-strengths-weaknesses) — Data Mining, chapter 5
- [Compare and contrast pollution in a city](https://www.bctengineer.com/question.md?key=semester_5%2Fcommunication_english%3Acompare-contrast-pollution-city-nepal) — Communication English, chapter 1
- [Why software reliability matters](https://www.bctengineer.com/question.md?key=semester_5%2Fsoftware_engineering%3Areliability-importance) — Software Engineering, chapter 9