SDLC Models (Waterfall, Agile, Spiral)

Software Development Life Cycle (SDLC)

The SDLC is a systematic process used by software engineers to design, develop, test, and maintain high-quality software. It provides a structured framework to ensure the software meets customer expectations and is completed within time and budget constraints.

1. Waterfall Model

• How it works: You must fully complete one phase (e.g., Requirements) before moving on to the next phase (e.g., Design). You cannot go backward.
• Pros: Simple to understand and manage. Best for small projects with extremely clear, unchanging requirements.
• Cons: Highly rigid. If a customer changes their mind halfway through, it is incredibly expensive and difficult to go back and rewrite code. Working software isn't seen until the very end.

2. Iterative & Incremental Model

• How it works: Instead of building the whole software at once, the software is divided into smaller chunks (increments). The team builds a small piece, tests it, and delivers it. Then they repeat (iterate) the process to add more features.
• Pros: Customers get to see working software early and can provide feedback.

3. Spiral Model

• How it works: The project loops through four phases (Objectives, Risk Assessment, Development/Testing, and Planning the next iteration) in a 'spiral' pattern.
• Pros: Excellent for large, complex, and high-risk projects (like banking or military software).
• Cons: Very expensive and requires highly skilled experts to accurately evaluate risks.

4. Agile Methodology

• How it works: Work is broken into short, 1-to-4 week cycles called Sprints. At the end of every Sprint, a working piece of software is delivered to the customer.
• Pros: Highly adaptable to changing requirements. If the customer wants a new feature, it can easily be added to the next Sprint. Promotes constant communication.
• Cons: Less emphasis on detailed documentation. Can easily go off-track if the customer's vision is unclear.
• Popular Frameworks: Scrum, Kanban.