Suggest an editImprove this articleRefine the answer for “What is SDLC and why is it needed? What are the main stages SDLC includes?”. Your changes go to moderation before they’re published.Approval requiredContentWhat you’re changing🇺🇸EN🇺🇦UAPreviewTitle (EN)Short answer (EN)**SDLC** is the overall cycle, and **SDLC models** are different ways of organizing it. They define in what order and how to move between stages. **Key point:** the choice of model depends on the project, requirements, and risks.Shown above the full answer for quick recall.Answer (EN)Image### What SDLC models exist and how do they differ? --- SDLC is the overall cycle, and **SDLC models** are different ways of organizing it. They define *in what order and how to move between stages*. The choice of model depends on the project, requirements, and risks. --- ### 1. **Waterfall** This is a linear model where each stage strictly follows the previous one. First requirements, then design, then code, then tests, and only then deployment. Changing something "after the fact" is hard - you have to go back up the "waterfall". Used where requirements are stable (for example, banking systems, government contracts). The main drawback is that flexibility is almost impossible if the client changes their mind. --- ### 2. **V-Model** Similar to Waterfall, but with an emphasis on testing. Each development stage (analysis, design, coding) is immediately linked to a verification stage (at the bottom of the letter "V"). For example, requirements have acceptance tests, design has integration tests. This improves quality but reduces flexibility. Used where full test coverage matters - medicine, aviation, defense. --- ### 3. **Spiral** The process runs in iterations - like the turns of a spiral. On each turn: risk analysis → design → development → testing → evaluation → next turn. It allows requirements to be refined gradually and risks to be reduced at early stages. Suitable for large and expensive systems where mistakes are very costly. --- ### 4. **Agile** Agile is not a single model but an entire philosophy, where development runs in short cycles - **iterations (sprints)**. Each sprint lasts 1-4 weeks and ends with a ready, working piece of the product. The team gets feedback, adjusts priorities, and moves on. Agile gives maximum flexibility but requires high discipline and constant communication. In practice, Scrum or Kanban is most often used. --- ### 5. **Iterative / Incremental** An intermediate option between waterfall and agile. The project is split into parts (iterations), each of which goes through all the SDLC stages - from analysis to testing. Each iteration adds new features, improving the product step by step. This reduces risks and allows a working product to be obtained already at early stages. --- ### Conclusion - **Waterfall** - strict and predictable, but inflexible. - **V-Model** - focus on testing and quality control. - **Spiral** - iterations plus risk analysis. - **Agile** - speed, flexibility, and constant adaptation. - **Iterative** - the product develops step by step, accumulating features. Each model solves one task: *making the development process manageable*, but in different ways.For the reviewerNote to the moderator (optional)Visible only to the moderator. Helps review go faster.