What defines the 'waterfall' software development model?

The waterfall software development model is characterized by its sequential and linear approach to software development, which is represented by clearly defined phases. Typically, these phases include requirements gathering, system design, implementation, testing, deployment, and maintenance. Each phase must be completed before moving on to the next, with little to no overlap between phases. This structured progression allows for thorough documentation and planning at each step, ensuring that all requirements are clearly understood and addressed before the project moves forward.

In contrast, iterative and incremental processes focus on repetition and gradual improvements, which is not a hallmark of the waterfall model. The notion of phases with no clear boundaries denotes a more flexible approach to software development, which waterflow does not adhere to. Additionally, agile methodologies emphasize adaptability and rapid iterations rather than the rigid sequential nature that defines the waterfall model. These distinctions illustrate why the choice linking the waterfall model to clearly defined phases with sequential progression is the correct interpretation of this software development approach.