CSS CS Optional — Paper-I, Section-B, Topic V.
🔥 Frequency: appeared in 4 of last 7 papers (2021, 2023, 2024, 2025).
🔑 The Models
- Waterfall: sequential — requirements → design → code → test → deploy → maintain. Simple, but late changes are expensive.
- Incremental: usable slices delivered one after another → see own page.
- RAD: component-based, time-boxed → see own page.
- Prototyping:
- Throwaway — discard prototype, rebuild from scratch.
- Evolutionary — refine the prototype into final system → see Evolutionary Model page.
- Spiral (Boehm): iterative + risk-driven. Four quadrants per loop:
- Determine objectives/alternatives/constraints
- Evaluate alternatives, resolve risks
- Develop & verify next-level product
- Plan next iteration
- Best for: large, high-risk, poorly-understood projects.
- V-Model: Waterfall + paired verification stage per phase (requirements↔acceptance testing, design↔system testing).
📊 Quick Comparison
|
Waterfall |
Spiral |
Agile |
| Structure |
Sequential |
Risk-driven loops |
Short sprints |
| Best for |
Fixed requirements |
Large/high-risk |
Evolving requirements |
| Cost of late change |
High |
Managed via risk analysis |
Low |
| Customer involvement |
Front-loaded only |
End of each loop |
Continuous |
🔥 Past Papers
- 2021 Q7(b) — Spiral model in detail (7 marks).
- 2025 MCQ — "iterative cycles + continuous development" → Agile.
⚠️ MCQ Trap
- "Iterative + risk-driven" → Spiral
- "Iterative + customer-collaborative, short sprints" → Agile