What is SDLC?
The Software Development Life Cycle (SDLC) is a structured process used by software teams to design, develop, test, and deliver high-quality software. It provides a step-by-step framework that ensures software meets business requirements efficiently.
Explore SDLC Models
Waterfall
Sequential, phase-by-phase. Simple and well-documented for stable requirements.
Agile
Iterative sprints with continuous delivery. Highly flexible and customer-focused.
Spiral
Risk-driven model combining iterative development with systematic prototyping.
Iterative
Build in cycles — each iteration adds or refines functionality progressively.
V-Model
Verification and Validation aligned — testing planned at every development stage.
Prototyping
Early working models gather feedback before the full system is built.
Core Phases of SDLC
Every SDLC model revolves around these fundamental phases. Click any phase to learn more.
1. Planning
Defines the project scope, timeline, budget, resources, and feasibility. A solid plan prevents costly mistakes downstream.
2. Requirements Analysis
Stakeholders and analysts gather functional and non-functional requirements. Output is a Software Requirements Specification (SRS).
3. System Design
Architecture, database schema, UI wireframes, and module structure are defined. Converts requirements into a blueprint.
4. Implementation (Coding)
Developers write code based on the design. Code reviews, version control, and coding standards are followed.
5. Testing & QA
Software is tested against requirements. Bugs are identified and fixed. Types include unit, integration, system, and UAT testing.
6. Deployment & Maintenance
Software is released to production. Post-deployment support handles bug fixes, performance tuning, and feature enhancements.
💧 Waterfall Model
The Waterfall model is the oldest and most straightforward SDLC approach. It follows a strict sequential flow — each phase must be fully completed before the next begins. Once a phase is finished, there is no going back (or it's costly to do so).
How it Works
✅ Advantages
- Simple and easy to understand
- Well-documented at every phase
- Easy to manage due to rigid structure
- Works well for small, well-defined projects
- Clear milestones and deliverables
❌ Disadvantages
- Inflexible to changing requirements
- Testing happens late — bugs are costly
- Poor model for complex, long-duration projects
- Customer sees product only at the end
- High risk for unclear or evolving requirements
Best Suited For
Example use cases: Building an embedded system for hardware with fixed specs, payroll software with well-defined rules, or government compliance systems.
Avoid when: Requirements are expected to change, the project is large and complex, or early user feedback is critical.
🔄 Agile Model
Agile is an iterative and incremental approach that delivers working software in short cycles called sprints (typically 1–4 weeks). It emphasizes collaboration, customer feedback, and adaptability.
Sprint Lifecycle
Backlog
Planning
Execution
Review
Product
Each sprint produces a potentially shippable increment. The cycle repeats until the product meets all goals.
Key Roles
- Product Owner — Defines priorities
- Scrum Master — Facilitates process
- Development Team — Builds the product
Key Artifacts
- Product Backlog — Full feature list
- Sprint Backlog — Current sprint tasks
- Burndown Chart — Progress tracking
The Agile Manifesto (2001)
Twelve principles, four core values:
over processes and tools
over comprehensive documentation
over contract negotiation
over following a plan
✅ Advantages
- High adaptability to changing requirements
- Continuous customer involvement
- Early and frequent delivery of value
- Reduced risk through incremental builds
- Encourages teamwork and accountability
❌ Disadvantages
- Harder to predict timeline & cost upfront
- Requires active customer participation
- Documentation can be neglected
- Scope creep risk if backlog is unmanaged
- Less effective for fixed-price contracts
🌀 Spiral Model
Proposed by Barry Boehm (1986), the Spiral model is risk-driven. It combines iterative development with the systematic aspects of Waterfall. Each loop (spiral) passes through four quadrants.
Four Quadrants of the Spiral
Objectives, Alternatives, Constraints
Identify & resolve risks
Design, Code, Test
Customer review & feedback
Each revolution of the spiral represents one development cycle
✅ Advantages
- Best model for risk management
- Suitable for large, complex projects
- Flexibility to add new requirements
- Users see the system early via prototypes
❌ Disadvantages
- Expensive — requires risk assessment expertise
- Not suitable for small, low-risk projects
- Complexity can make management difficult
- End date is difficult to predict
🔁 Iterative Model
The Iterative model starts with a simple initial implementation and then progressively enhances it through iterations. Unlike Agile, it doesn't always require continuous customer involvement after each cycle.
Iteration Flow
✅ Advantages
- Partial working versions released early
- Easier to test and debug per iteration
- Changes can be incorporated in next iteration
- Lower initial delivery risk
❌ Disadvantages
- Total cost can be higher than Waterfall
- May not be suitable if requirements are unclear
- Requires good planning for iterations
- Architecture issues may surface late
✅ V-Model (Verification & Validation)
The V-Model extends the Waterfall model. Each development phase on the left arm has a corresponding testing phase on the right arm. Testing is planned parallel to development — not as an afterthought.
The V-Shape Diagram
Dashed lines show which test phase verifies each development phase
✅ Advantages
- Defects found early due to parallel planning
- Simple and easy to manage
- Works well when requirements are well-defined
- Every phase has specific deliverables
❌ Disadvantages
- Very rigid — no mid-phase flexibility
- No working software until late
- Not suitable for changing requirements
- Difficult to adapt to complex projects
🧪 Prototyping Model
In this model, a working prototype of the system is built early to gather user feedback before the actual product is developed. Especially useful when requirements are unclear.
Prototyping Lifecycle
Types of Prototyping
- Throwaway — Prototype is discarded
- Evolutionary — Prototype evolves into final system
- Incremental — Multiple prototypes built
- Extreme — Rapid UI focus, then backend
✅ / ❌
Pros: Early user feedback, reduces misunderstandings, clear requirements.
Cons: Can lead to scope creep; prototype may set wrong expectations; time-consuming iterations.
📊 Model Comparison
Quick reference to choose the right SDLC model for your project.
| Model | Requirements | Flexibility | Testing | Customer Involvement | Best For |
|---|---|---|---|---|---|
| 💧 Waterfall | Fixed & clear | ❌ Very Low | Late (after coding) | Low | Small, stable projects |
| 🔄 Agile | Evolving | ✅ Very High | Each sprint | Continuous | Dynamic, customer-driven |
| 🌀 Spiral | Partially known | ✅ High | Each spiral | High | High-risk, large projects |
| 🔁 Iterative | Partially known | 🔶 Medium | Each iteration | Medium | Projects needing refinement |
| ✅ V-Model | Fixed & clear | ❌ Very Low | Parallel (each phase) | Low | Safety-critical systems |
| 🧪 Prototyping | Unclear/fuzzy | ✅ High | Per prototype | Very High | UI-heavy, unclear needs |
How to Choose?
→ Waterfall or V-Model
→ Agile or Iterative
→ Spiral
→ Prototyping
🎯 SDLC Quiz
Test your knowledge of SDLC models and concepts.