The most common way of thinking of the SDLC is the waterfall model within which phases of activity are defined based on the thought processes required to conduct the activities (see Figure 1) (Royce, 1972). Output of each phase is input to the next phase. Phases historically included the following with the key focus in parentheses: feasibility (readiness), analysis (what), design (how), detailed design (how), coding and unit testing (technology), testing (correctness), and implementation (transition to operation). On-going maintenance accounts for about 80% of an application’s life cycle cost and follows each phase but with a narrower scope than the whole application. In this model, application development ceases at implementation with little attention to use of the application in its various contexts.
Waterfall software development phases (Adapted from Royce, 1970)