Unit 11.1C · Term 1

SDLC Models

The Software Development Life Cycle (SDLC) describes the stages a software project goes through from idea to deployment. Different models organise these stages in different ways depending on project needs.

Learning Objectives

11.2.1.1 Describe the stages of the SDLC
11.2.1.2 Compare cyclical, waterfall, and spiral models

Lesson Presentation

11.1C-sdlc-models.pdf · Slides for classroom use

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Conceptual Anchor

The House-Building Analogy

Building software is like building a house. You need to: understand what the client wants (analysis), draw blueprints (design), build it (implementation), check for faults (testing), move the client in (deployment), and fix problems over time (maintenance). The SDLC is the blueprint for this entire process.

Rules & Theory

SDLC Stages

Stage	Purpose	Key Activities
1. Analysis	Understand the problem	Gather requirements, interview users, feasibility study
2. Design	Plan the solution	System architecture, UI mockups, data structures, DFDs
3. Implementation	Build the system	Write code, create database, build interfaces
4. Testing	Verify correctness	Unit tests, integration tests, user acceptance testing
5. Deployment	Release to users	Install, train users, migrate data
6. Maintenance	Keep it running	Fix bugs, add features, update for new OS

SDLC Models Compared

Feature	Waterfall	Spiral	Iterative (Cyclical)
Flow	Linear, top-down	Loops with risk analysis	Repeated cycles
Going back	Cannot go back easily	Each loop revisits stages	Each cycle improves the product
Risk handling	Risks found late	Risk analysis each cycle	Risks reduced each iteration
Client involvement	Beginning and end only	Each spiral reviewed	Feedback every cycle
Best for	Small, well-defined projects	Large, high-risk projects	Projects with changing requirements
Disadvantage	Inflexible, no backtracking	Complex, expensive	Scope creep risk

Visual Models

WATERFALL:                 SPIRAL:                    ITERATIVE:
  Analysis                  ┌─ Plan ──┐                 ┌─ Cycle 1 ─┐
    ↓                       │         │                 │ Analyze    │
  Design                    ↓         ↓                 │ Design     │
    ↓                     Risk ←── Develop               │ Build      │
  Implementation          Analysis    ↓                 │ Test       │
    ↓                       │      Evaluate              └───┬───────┘
  Testing                   └──────────┘                     ↓
    ↓                     (repeats, getting               ┌─ Cycle 2 ─┐
  Deployment              larger each loop)              │ Improve    │
    ↓                                                    │ Add features│
  Maintenance                                            └───┬───────┘
                                                             ↓ ...

Agile ≈ Modern Iterative

Modern software companies use Agile methodologies (Scrum, Kanban) which are iterative. They work in 2-week "sprints", delivering working software each cycle and adapting to changing requirements.

Common Pitfalls

Waterfall is Outdated/Bad

Waterfall is still used successfully for projects with fixed, well-understood requirements (e.g. building a bridge, military systems). It's only "bad" when requirements change frequently.

Tasks

Remember

List the 6 stages of the SDLC in order.

Understand

Explain why the waterfall model is unsuitable for a startup building a new social media app.

Analyze

A hospital needs a patient management system. Which SDLC model would you recommend and why?

Self-Check Quiz

Q1: What are the 6 stages of the SDLC?

Analysis, Design, Implementation, Testing, Deployment, Maintenance.

Q2: What is the key feature of the spiral model?

Risk analysis at each iteration — the project loops through planning, risk analysis, development, and evaluation.

Q3: When is the waterfall model most appropriate?

When requirements are well-defined and unlikely to change (e.g., small, fixed-scope projects).