Software Development Methodologies

This lesson covers the major software development methodologies — structured approaches to planning, building, testing, and deploying software systems. Understanding these methodologies is essential for the A-Level Computer Science paper on software development and project management.

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Why Use a Methodology?

Developing software without a structured approach leads to:

• Missed deadlines and budget overruns
• Software that does not meet user requirements
• Difficult-to-maintain code
• Poor quality and unreliable systems

A software development methodology provides a framework that guides the development process, ensuring projects are completed on time, within budget, and to specification.

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The Waterfall Model

The Waterfall model is a linear, sequential approach where each phase must be completed before the next begins. There is no going back to a previous phase once it is complete.

Phases

Phase	Description
Requirements	Gather and document all requirements from the client.
Design	Plan the system architecture, data structures, and interfaces.
Implementation	Write the code according to the design.
Testing	Test the system against the requirements.
Deployment	Release the system to users.
Maintenance	Fix bugs and make updates after deployment.

Requirements → Design → Implementation → Testing → Deployment → Maintenance

Advantages

• Simple and easy to understand.
• Well-documented at each stage.
• Works well for projects with well-defined, stable requirements.
• Easy to manage due to its rigid structure.

Disadvantages

• No flexibility to go back — changes are costly.
• Users do not see the product until late in the process.
• Not suitable for projects where requirements may change.
• Testing occurs late, so bugs found late are expensive to fix.

Best For

• Large, well-understood projects (e.g., government systems, safety-critical software).
• Projects where requirements are unlikely to change.

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The Agile Methodology

Agile is an iterative and incremental approach that delivers software in small, working increments called sprints (typically 1-4 weeks). It emphasises collaboration, flexibility, and responding to change.

The Agile Manifesto (Key Values)

Agile Values	Over
Individuals and interactions	Processes and tools
Working software	Comprehensive documentation
Customer collaboration	Contract negotiation
Responding to change	Following a plan

How Agile Works

1. Requirements are gathered and prioritised in a product backlog.
2. A small set of features is selected for the next sprint.
3. The team designs, builds, and tests those features.
4. A working increment is delivered and demonstrated to the client.
5. Feedback is gathered, and the backlog is updated.
6. The cycle repeats until the project is complete.

Advantages

• Flexible — adapts to changing requirements.
• Frequent delivery of working software.
• Regular client feedback ensures the product meets needs.
• Issues are identified and resolved early.

Disadvantages

• Requires active client involvement throughout.
• Can be difficult to predict timelines and costs.
• Less emphasis on documentation can cause issues for large teams.
• Scope creep — the project can expand beyond original plans.

Best For

• Projects with evolving or unclear requirements.
• Web and mobile applications.
• Startups and innovative products.

Exam Tip: Do not confuse Agile with Scrum. Agile is a philosophy (a set of values and principles). Scrum is a specific framework that implements Agile practices. In the exam, if asked about Agile, focus on the iterative approach, sprints, and client collaboration.

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The Spiral Model

The Spiral model combines elements of the Waterfall model with iterative prototyping and adds a strong emphasis on risk analysis. Development proceeds in a series of cycles (spirals), each with four phases.

Phases of Each Spiral