Software Development Lifecycle – SS3 Digital Technologies Lesson Note (First Term)

The Software Development Life Cycle (SDLC) is a step-by-step process that teams follow to build high-quality software that works and satisfies the customer. It has six phases: planning, analysis, design, implementation, testing, and deployment and maintenance. Teams follow it using models such as Waterfall, which moves in one direction, and Agile, which works in short sprints.

Behavioural objectives

By the end of the lesson, students should be able to:

• State what the SDLC is and why teams use it.
• List and describe the six phases of the SDLC.
• Explain how the Waterfall model works, with its strength and weakness.
• Explain how the Agile model works and what a sprint is.
• Compare Waterfall and Agile and say when each is best used.

What is the SDLC? (The “game plan”)

Cooking a complex meal or building a piece of furniture without instructions usually ends in a mess.

In professional programming, we do not just sit down and start typing code. We use a “game plan” called the Software Development Life Cycle (SDLC). It is a step-by-step process that teams follow to build high-quality software that actually works and makes the customer happy.

Think of it as a map. It tells us:

1. Where to start.
2. What to do next.
3. How to know when we are finished.

Without the SDLC, software would be full of bugs, over budget and late.

What are the six phases of the SDLC?

Every piece of software, from WhatsApp to TikTok, goes through these six stages:

1. Planning: “What are we building and why?” We define the goal and see if we have the money and time to do it.
2. Analysis: We talk to the users. “What buttons do you need? What problem are we solving for you?”
3. Design: This is the blueprint phase. We do not code yet. We draw how the screens look and how the data flows.
4. Implementation (coding): This is where the programmers write the actual code based on the design.
5. Testing: We try to “break” the software. We look for bugs and fix them before the public sees the app.
6. Deployment and maintenance: We release the app to the world. If users find new bugs or want new features later, we update it.

What is the Waterfall model? (The “one-way street”)

The Waterfall model is the oldest way of building software. Just like a real waterfall, the water only flows down. You cannot move to the next stage until the current one is 100% finished. The whole project runs as a straight line from start to finish.

• How it works: You plan everything at the start, design everything, then code everything.
• The good: It is very disciplined and easy to manage because everyone knows exactly what phase they are in.
• The bad: It is very “stiff”. If you realise you made a mistake in the planning phase while you are already coding, it is very expensive and difficult to go back up the waterfall.

Best for: Small projects where you know exactly what you want from Day 1.

What is the Agile model? (The “building blocks”)

In the modern world, things change fast. Agile was created because the Waterfall model was too slow. Instead of building the whole app at once, Agile breaks the project into tiny pieces called sprints (usually 2 to 4 weeks long).

• How it works: You build a small, working part of the app, show it to the customer, get their feedback, and then move to the next part.
• The “cycle”: Every two weeks, you plan, design, code and test. It is like a mini-SDLC happening over and over again, as a series of small loops.

The main advantage: If the customer changes their mind halfway through, it is easy to pivot because you have not built the whole thing yet. Agile is all about flexibility.

Waterfall or Agile: which one should you pick?

Choosing a model is like choosing a vehicle. You would not take a bicycle on a highway, and you would not take a semi-truck to buy a loaf of bread.

Evaluation

1. What does SDLC stand for, and why do teams use it?
2. List the six phases of the SDLC in order.
3. Why is it expensive to correct a planning mistake in the Waterfall model?
4. What is a sprint in the Agile model?
5. State two differences between Waterfall and Agile.

Assignment

1. In your own words, describe what happens in the design phase and in the testing phase.
2. A customer is likely to change their mind often during a project. Say which model, Waterfall or Agile, suits this project better, and give two reasons.