SDLC

Every piece of software, whatever the methodology, goes through the same kinds of work. Planning decides what to build and why; requirements describe what it must do; design decides how; implementation writes the code; testing checks it; deployment releases it to users; and maintenance fixes bugs, updates dependencies and adds features for as long as it is in use, which is usually the longest phase.

SDLC models differ in how they arrange those stages. The waterfall model runs them once, in order. The V-model pairs each design stage with a matching test stage. Iterative and spiral models repeat the cycle in rounds, reducing risk step by step. Agile methods such as Scrum run through all the stages in short iterations of a few weeks, delivering working software each time, and DevOps extends the cycle into continuous delivery and operations.

Organizations formalize the SDLC to make work predictable and auditable: who approves requirements, what reviews happen before release, how changes are tracked. A secure SDLC adds security activities to every stage, such as threat modeling during design, static analysis during implementation, penetration testing before release and patching during maintenance.

A common misconception is that the SDLC is just another name for waterfall. It describes the stages themselves, which every approach covers in some form; the models only differ in their order, size and how often they repeat. Choosing a model is about matching the process to the project's risk, uncertainty and need for feedback.