Software lifecycle
CIE A-Level Computer ScienceΒ· 20 min read
1. Core Stages of All Software Lifecyclesβ β ββββ± 5 min
All software lifecycle models are structured frameworks for building and maintaining software. Regardless of the specific model used, they all share core high-level stages that map the process from initial idea to final retirement.
Software Lifecycle
A structured framework that describes all stages involved in developing, deploying, and maintaining a software product from initial conception to final retirement.
Stage | Key Activities |
|---|---|
Feasibility | Assess technical, financial, operational project viability |
Requirements analysis | Gather and document required software functionality |
Design | Plan architecture, data structures and user interfaces |
Implementation | Write code and build the working software |
Testing | Verify requirements are met and fix defects |
Deployment | Release software to end users |
Maintenance & Retirement | Update/fix software, retire when obsolete |
List the core stages of the software lifecycle that occur after a feasibility study is approved, and before deployment.
- 1
- After feasibility approval, the first stage is requirements analysis. The team meets with stakeholders to gather and document all functional and non-functional requirements, which are then signed off.
- 2
- Next, the design stage produces architecture diagrams, database schemas, and interface mockups that meet the documented requirements.
- 3
- Implementation follows, where developers write code based on the design specifications to build the software.
- 4
- Finally, testing verifies that the software works as required and fixes all identified defects, before progressing to deployment.
2. The Waterfall Modelβ β ββββ± 5 min
The Waterfall model is the original traditional sequential lifecycle model, where each stage is completed fully in order, and you cannot return to a previous stage once it is finished.
Waterfall Model
A linear, sequential lifecycle model where each stage is completed fully before progressing to the next, with no built-in backtracking or iteration.
Example:
Used for small, low-risk projects with completely fixed, agreed requirements where changes are not expected.
A small local business needs a simple static website, with all requirements fixed and agreed in writing. Explain why the Waterfall model is appropriate for this project.
- 1
- Waterfall is ideal for small projects with stable, fixed requirements, which matches the description of this project.
- 2
- Waterfall has very low administrative overhead compared to iterative models, making it efficient and cost-effective for a low-budget small project.
- 3
- No changes are expected after requirements are agreed, so there is no need for the flexibility of an iterative model. The project can be completed quickly in a single sequential pass.
Exam tip:
In CIE exams, always link the properties of the model to the specific scenario when justifying your choice, to earn full marks.
3. Iterative, Incremental and Agile Modelsβ β β βββ± 6 min
Iterative models break development into repeated cycles, refining the product each cycle to incorporate feedback. Incremental models deliver working software in small, functional chunks, adding new features each cycle. Modern Agile methodologies (like Scrum) combine both approaches.
Agile Software Development
A flexible, iterative approach to software development that prioritizes rapid delivery of working software, responding to changing requirements, and continuous customer feedback.
A startup is building a new consumer mobile app, and needs to release new features monthly to respond to user feedback and changing market trends. Justify why Agile is the right model here.
- 1
- Agile uses short 2-4 week development cycles (sprints) that allow the team to deliver new working features every month, matching the startup's requirement for regular releases.
- 2
- Agile is designed to accommodate changing requirements, so the team can easily incorporate user feedback and market changes into future sprints.
- 3
- Early delivery of working software allows the startup to test the product with real users early, reducing the risk of building a product that does not meet market needs.
4. Spiral and RAD Modelsβ β β β ββ± 4 min
Two other common models tested in CIE 9618 are the Spiral model (for high-risk projects) and Rapid Application Development (RAD, for fast, user-focused development). The Spiral model combines Waterfall structure with iterative development and a strong focus on risk management.
Spiral Model
A risk-driven iterative lifecycle model that requires a formal risk assessment and mitigation step before each new development cycle.
A large aerospace company is developing new safety-critical flight control software for commercial aircraft. Which lifecycle model is most suitable, and why?
- 1
- The Spiral model is the most suitable choice for this project.
- 2
- This is a large, high-risk project: any software defect could have catastrophic consequences, so rigorous risk analysis is required before every development stage.
- 3
- The Spiral model requires explicit risk identification and mitigation at the start of each cycle, which matches the safety requirements of this project.
- 4
- Repeated prototyping and testing in each spiral cycle also reduces the chance of critical defects being missed, which is essential for a safety-critical system.
5. Common Pitfalls
Wrong move:
Claiming Agile does not include all core software lifecycle stages
Why:
All core stages are still completed in Agile, just repeated incrementally across sprints instead of done once at the start
Correct move:
State that core stages are repeated for each increment, rather than omitted entirely
Wrong move:
Claiming Waterfall is never used in modern development
Why:
Waterfall is still appropriate for small projects with completely fixed requirements and low overhead needs
Correct move:
Justify Waterfall for small, fixed-requirement scenarios where iteration is unnecessary
Wrong move:
Confusing incremental and iterative development
Why:
The terms describe different concepts, even though modern models combine both
Correct move:
Remember: incremental = adding new functionality in chunks, iterative = refining the product through repeated cycles
Wrong move:
Selecting Agile for all large projects
Why:
Agile lacks the rigorous documentation and formal risk analysis required for regulated safety-critical projects
Correct move:
Select Spiral or Waterfall for safety-critical, regulated projects with fixed requirements
Wrong move:
Forgetting to include maintenance as a core lifecycle stage
Why:
Most software spends most of its lifetime in the maintenance stage after deployment
Correct move:
Always include maintenance (and eventual retirement) when listing lifecycle stages in exams
6. Quick Reference Cheatsheet
Model | Best For | Key Advantage | Key Disadvantage |
|---|---|---|---|
Waterfall | Small, fixed requirements, low risk | Simple, low overhead, clear documentation | Cannot handle changes, late testing |
Agile | Dynamic requirements, consumer products | Fast delivery, adapts to change | Higher overhead, less formal documentation |
Spiral | Large, high-risk, safety-critical projects | Explicit risk management | Time-consuming and expensive |
RAD | Fast development, user-focused projects | Quick delivery, early user feedback | Poor focus on non-functional requirements |
When this came up on past exams
AI-estimated based on syllabus patterns β cross-check with official past papers for accuracy. Use only as revision-focus signals.
- 2022 Β· 1
Justify model selection scenario
- 2023 Β· 1
Compare Waterfall and Agile
- 2024 Β· 1
Describe Spiral model use case
What's Next
Understanding software lifecycle models is a foundational topic for CIE 9618 Paper 1, and is assessed almost every year in both multiple choice and structured response questions. You will often be asked to select and justify a model for a given scenario, so practicing matching model properties to scenario characteristics is key to earning full marks. This knowledge underpins all subsequent software development topics, where you will explore individual lifecycle stages in more detail for exam assessment.