Although many life-cycle models emphasize
the requirements phase as an upfront activity, it is
actually an iterative one that continues throughout
the entire lifetime of the project [3,4].
Requirements drive not only the initial design and
validation of the system, but support ongoing
activities such as change management, regression
test selection, and compliance monitoring. The
requirements process can be described by the five
primary disciplines of requirements elicitation,
analysis, specification, validation, and
management. Although there is overlap between
these activities they are described here as
individual phases for pedagogical purposes.