Software Development Life Cycle (SDLC) Models

1. Waterfall Model

The Waterfall model is a linear-sequential approach where each phase must be completed before the next begins. Outputs from one phase act as inputs to the next. It is simple and easy to manage but inflexible — changes are costly once a phase is complete.

2. Iterative Waterfall Model

An extension of Waterfall that allows feedback loops between phases. It provides limited opportunities to revisit earlier phases (except feasibility). Useful when requirements may evolve but still relatively structured.

3. Agile Model

Agile divides work into small, time-boxed iterations (sprints). Each iteration includes planning, design, coding, testing and review. Agile emphasises customer collaboration, adaptability and frequent delivery of working software.

4. Spiral Model

The Spiral model combines iterative development with systematic risk analysis. Development proceeds in spirals (iterations) with phases like planning, risk analysis, engineering and evaluation. Suitable for large, high-risk projects.

5. Prototype Model

In the Prototype model, a prototype (working model) is built early to clarify requirements. The customer evaluates the prototype and provides feedback, which guides the final implementation. This reduces misunderstandings but may add extra effort if many prototypes are needed.

6. V-Model

The V-model (Verification & Validation) is an extension of Waterfall where each development phase has a corresponding testing phase. It emphasises traceability and early test planning.

7. RAD (Rapid Application Development) Model

RAD focuses on rapid prototyping and iterative delivery. Projects are split into modules developed in parallel; completed modules are integrated into the final system. RAD is good for projects with clear modularisation and requirements that can be rapidly developed.