What is the Waterfall model in software project methodology?

The Waterfall model is a linear, sequential approach to project execution: each phase (requirements, design, development, testing, deployment) must be fully completed before the next one begins, flowing downward like a waterfall, with little to no going back to revisit an earlier phase once it's finished.

flowchart TD
    A[Requirements] --> B[Design]
    B --> C[Development]
    C --> D[Testing]
    D --> E[Deployment]

Traditional SAP implementation projects historically followed a Waterfall-influenced structure, since the scope of an ERP rollout (which modules, which business processes) is typically defined upfront before configuration and development begin in earnest. Its main strength is predictability — clear milestones and a defined end state — while its main weakness is inflexibility if requirements change significantly partway through, since revisiting an earlier phase is costly once later phases are already underway.

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