It is rare for the waterfall style of model to show the various activities that occur across all life-cycle phases. For example, the diagram omits important activities such as project management, quality management, and configuration control. A further weakness of many waterfall models is the treatment of maintenance. Maintenance in this example is shown as a single box: this is the view of a system as perceived by the supplier, and particularly a supplier who has no responsibility for software maintenance. In reality each maintenance action will follow the full life cycle from feasibility through to implementation.
See also spiral model, V-model.
"waterfall model." A Dictionary of Computing. . Encyclopedia.com. (March 19, 2019). https://www.encyclopedia.com/computing/dictionaries-thesauruses-pictures-and-press-releases/waterfall-model
"waterfall model." A Dictionary of Computing. . Retrieved March 19, 2019 from Encyclopedia.com: https://www.encyclopedia.com/computing/dictionaries-thesauruses-pictures-and-press-releases/waterfall-model