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What Is the SDLC? A Software System's Life from Idea to Retirement

The SDLC (Software Development Life Cycle) is the full set of phases software goes through from idea to retirement: requirements, design, implementation, test, deployment, operations and retirement; models don't change the phases, only their order and repetition. Using Bookstore's returns feature we look at each phase's output, the weight of maintenance, the four process groups of ISO/IEC/IEEE 12207:2026 and the forgotten retirement phase.