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4.4 Requirements engineering processes 99

Requirements
Specification

System Requirements
Specification and
Modeling

User Requirements
Specification

Business Requirements
Specification

Start
Feasibility
System Study
Requirements Req. Requirements
Elicitation Elicitation User Validation
Requirements
Elicitation Prototyping

Reviews

Figure 4.12 A spiral
view of the
requirements System Requirements
engineering process Document

4.4 Requirements engineering processes

As I discussed in Chapter 2, requirements engineering processes may include four
high-level activities. These focus on assessing if the system is useful to the business
(feasibility study), discovering requirements (elicitation and analysis), converting
these requirements into some standard form (specification), and checking that the
requirements actually define the system that the customer wants (validation). I have
shown these as sequential processes in Figure 2.6. However, in practice, require-
ments engineering is an iterative process in which the activities are interleaved.
Figure 4.12 shows this interleaving. The activities are organized as an iterative
process around a spiral, with the output being a system requirements document.
The amount of time and effort devoted to each activity in each iteration depends on
the stage of the overall process and the type of system being developed. Early in
the process, most effort will be spent on understanding high-level business and