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This chapter describes key systems development models, their purpose, and why it is important to use them. This chapter also presents project development strategies of methods for evolving the system over time.
Models for systems development are important because they:
Models for the systems and software development have been depicted in two principal forms. The Waterfall development model was first described in 1969 [Win Royce] for systems with software components [see Figure 4‑1]. The Spiral model was described in 1983 [Barry Boehm] for risk reduction in software developments [see Figure 4‑2]. These two models are still the foundation for systems and software development.
In 1988, National Aeronautics and Space Administration [NASA] saw a benefit in bending the Waterfall model into the "V" shape for software development. This was the original Vee technical model as shown in Figure 4‑3. In 1990, Kevin Forsberg and Hal Mooz created an enhanced version of the Vee model that integrated the best aspects of the Waterfall and the Spiral development models. A general case development model for systems was created by adding an emphasis on risk, opportunity, and stakeholder involvement. It augmented the Vee with a development strategy [iterative/ evolutionary development features]. This is a departure from the previous models which focused on software. The Forsberg and Mooz Vee model was published after the NASA model in October 1991 at the INCOSE [National Council on Systems Engineering] symposium in Tennessee. Since then, the Vee Development Model has become widely accepted and is illustrated [in some form] in both the EIA 632 and ISO 15288 systems engineering process standards. Currently, this model is being adopted throughout the broad spectrum of systems development environments.
The following are some observations on the Waterfall, Spiral, and Vee development models.