The SDLC describes activities and functions that all systems developers perform, regardless of which
approach they use. In the waterfall model, the result of each phase is called a
deliverable, or end product, which flows into the next phase Some analysts see a disadvantage
in the built-in structure of the SDLC, because the waterfall model does not
emphasize interactivity among the phases. This criticism can be valid if the SDLC
phases are followed too rigidly. However, adjacent phases usually interact, as shown by the dotted lines in Figure 1-27 and interaction among several phases is not
uncommon. Other analysts regard the waterfall model as a two-way water flow
model, with emphasis on iteration and user input. Used in this manner, the traditional
model is not as different from agile methods as it might appear to be.
The SDLC model usually includes five steps, which are described in the following
sections: systems planning, systems analysis, systems design, systems implementation,
and systems support and security