1. Basics / Fundamentals

🌀 Software Development Life Cycle (SDLC) Models

SDLC (Software Development Life Cycle) ek structured process hai jo software banane ke liye follow kiya jata hai. Isme step-by-step stages hote hain jaise:
👉 Requirement → Design → Development → Testing → Deployment → Maintenance

Different models use hote hain SDLC ko implement karne ke liye.

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1️⃣ Waterfall Model

• Definition: Step-by-step linear approach, jisme har stage complete hone ke baad hi next stage start hoti hai.

• Phases: Requirement → Design → Implementation → Testing → Deployment → Maintenance

• Pros: Simple, easy to use, clear documentation.

• Cons: Changes karna mushkil, testing late stage me hoti hai.

• Best for: Small projects with clear requirements.

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2️⃣ Agile Model

• Definition: Iterative & incremental model, project ko small sprints me divide kiya jata hai (2–4 weeks).

• Pros: Fast delivery, customer feedback early milta hai, flexible.

• Cons: Documentation kam hoti hai, skilled team chahiye.

• Best for: Dynamic projects with frequently changing requirements.

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3️⃣ Spiral Model                          

• Definition: Combination of Waterfall + Prototyping, project ko phases me develop karte hain but har phase ke baad risk analysis hota hai.

• Pros: Risk management strong, big projects ke liye suitable.

• Cons: Costly, complex, experienced team chahiye.

• Best for: Large, high-risk projects (like defense, banking systems).

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4️⃣ V-Model (Verification & Validation Model                  

• Definition: Extension of Waterfall, jisme har development stage ke sath ek testing stage linked hoti hai.

• Pros: Bugs early detect hote hain, structured testing.

• Cons: Rigid, changes handle karna difficult.

• Best for: Safety-critical projects (medical software, embedded systems).

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📊 Comparison Table

Model	Approach	Flexibility	Best For
Waterfall	Linear	❌ Low	Small projects
Agile	Iterative	✅ High	Changing requirements
Spiral	Iterative + Risk	✅ High	Large, risky projects
V-Model	Linear + Testing	❌ Medium	Safety-critical projects

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👉 Short me:

• Waterfall = Simple, step-by-step

• Agile = Flexible, fast, customer feedback

• Spiral = Risk-focused, costly

• V-Model = Testing-focused, rigid