Development Models (Cambridge (CIE) A Level Computer Science): Revision Note
Exam code: 9618
Waterfall
What is the waterfall model?
The Waterfall Model is a sequential software development process divided into distinct phases
Each phase must be completed before the next one begins
Steps
Requirement Gathering and Analysis: All possible system requirements to be developed are captured and documented clearly
System Design: The requirements are translated into a design. Architects and designers define the overall architecture and identify the main components
Implementation: The actual code is written in this phase based on the design documents, turning the system design into a functional program
Integration and Testing: All the components and modules are integrated and tested to ensure that the entire system works as expected
Deployment: The product is released to the market or handed over to the client. It may involve installation, customization, and training
Maintenance: Post-release, the system needs regular maintenance to fix bugs, improve performance, or add new features
The Waterfall Model in Software Engineering
Benefits and drawbacks
Benefits | Drawbacks |
|---|---|
Simple and linear – easy to understand and follow | Inflexible – difficult to make changes once development begins |
Clear stages and milestones – easy to track progress | Expensive to fix late problems – issues found late are harder to resolve |
Ideal for well-defined projects – works best when requirements are fixed | Long development cycle – each stage must be completed before moving on |
Suitability
The Waterfall Model is most suitable for projects where requirements are well understood and unlikely to change
It works well when high quality and compliance are essential, and there is a clear understanding of the project's goals and constraints
Iterative (Agile)
What is the iterative model?
The iterative model s a type of Agile software development methodology that promotes adaptability and high customer involvement
Steps
Identify user stories and requirements
Work closely with stakeholders to gather functional and non-functional requirements
Requirements are often written as user stories (e.g. As a user, I want to...)
Plan the sprint (Sprint Planning)
Break down requirements into tasks
Choose a set of tasks (features) for the current sprint (a short time-boxed development period, usually 1–4 weeks)
Define the sprint goal
Design the solution
Decide how the selected features will be built
Focus is on simple and adaptable design, not heavy upfront documentation
Develop the features
Write code for the selected tasks in the sprint
Developers often work in pairs or small teams (e.g. pair programming)
Test continuously
Perform unit testing, integration testing, and acceptance testing during the sprint
Testing is ongoing, not saved for the end
Review progress (Sprint Review)
Demo the working software to stakeholders
Collect feedback and identify changes or improvements
Reflect on process (Sprint Retrospective)
The team reflects on what went well and what needs improving in the next sprint
Focus is on team performance and process optimisation
Release (may happen after every sprint or set of sprints)
Deploy working software to users or staging environment
Repeat
Move to the next sprint with updated priorities and feedback
Benefits and drawbacks
Benefits | Drawbacks |
|---|---|
Highly adaptable – responds quickly to changing requirements | Requires experienced team members – may be hard to manage without expertise |
Frequent communication – promotes constant collaboration | Risk of burnout – intense collaboration can tire the team |
Focus on quality – encourages good design and continuous testing | May lack documentation – flexibility can reduce written records |
Customer collaboration – ensures the product meets real needs | Scope creep – changing goals may lead to uncontrolled growth |
Suitability
The iterative model is most suitable for small to medium-sized projects where requirements can change and customer involvement is high
Rapid Application Development (RAD)
What is RAD?
Rapid Application Development (RAD) is a software development methodology that emphasises fast and iterative development
Steps
Requirement planning: Gather general system requirements, define constraints and assumptions
User design and prototyping: Collaborate with users to develop prototypes, ensuring alignment with user needs
Construction or iterative development: Build the system incrementally, with continuous user feedback and adaptation
Cutover or deployment: Transition the product into the live environment, including user training, support, and documentation
Maintenance and updates: Continue to adapt and improve the system based on user feedback and needs
Rapid Application Development (RAD) Model of Software Development
Benefits and drawbacks
Benefits | Drawbacks |
|---|---|
Speed – fast development and delivery at relatively low cost | Requires strong team collaboration – skilled and cohesive teams are essential |
User involvement – client feedback shapes the system throughout | Potential quality issues – speed may reduce testing and documentation |
Flexibility – adapts quickly to changing requirements | Not ideal for small projects – may be too complex for simple systems |
Incremental development – builds in small, testable parts | Scope creep risk – flexibility can lead to ever-expanding requirements |
Suitability
Rapid Application Development is most suitable for projects where rapid delivery is required and where requirements can be developed and refined on the go
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