A Software Development Life Cycle (SDLC) model defines the phases of software development and the order in which they are carried out. Choosing the right model is crucial to project success.
💡 Why Do We Need a Life Cycle Model?
Provides a structured framework for development
Defines clear milestones and deliverables
Helps in project planning, tracking, and cost estimation
Improves communication between team members and clients
Reduces risk of project failure
💧 Classical Waterfall Model
The oldest and most widely known SDLC model. Each phase must be completed before the next begins — like water flowing downward, with no going back.
Classical Waterfall Model
Advantages
Simple and easy to understand
Well-documented phases
Works well for small, fixed-requirement projects
Disadvantages
No feedback loops — hard to go back
Poor fit for changing requirements
Testing happens very late
High risk for complex systems
🔄 Iterative Waterfall Model
An improvement over classical waterfall — allows feedback loops between adjacent phases. If a problem is found in phase N, you can go back to phase N-1.
Key difference: Feedback arrows going upward between phases allow limited backtracking. Errors are caught earlier compared to classical waterfall.
Each phase can send feedback to the previous one
More realistic than classical waterfall
Still somewhat rigid — not suitable for heavily evolving requirements
🧪 Prototype Model
A working model (prototype) of the system is built quickly to help the client visualize the final product and refine requirements.
Prototype Development Cycle
When to Use
Requirements are unclear or incomplete
UI/UX is critical to the project
Client wants to see early results
Limitations
Prototype may raise unrealistic expectations
Can lead to incomplete documentation
Prototype quality may be mistaken for final quality
🌀 Spiral Model
Proposed by Barry Boehm (1988). Combines elements of both iterative development and the systematic aspects of the waterfall model with a strong focus on risk management.
Spiral Model — 4 Quadrants per Loop
Four Quadrants of Each Loop
Quadrant 1
Planning
Determine objectives, alternatives, constraints
Quadrant 2
Risk Analysis
Identify & resolve risks, build prototype if needed