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102 Chapter 4 Requirements engineering

4. Requirements specification The requirements are documented and input into the
next round of the spiral. Formal or informal requirements documents may be
produced, as discussed in Section 4.3.

Figure 4.13 shows that requirements elicitation and analysis is an iterative
process with continual feedback from each activity to other activities. The process
cycle starts with requirements discovery and ends with the requirements documenta-
tion. The analyst’s understanding of the requirements improves with each round of
the cycle. The cycle ends when the requirements document is complete.
Eliciting and understanding requirements from system stakeholders is a difficult
process for several reasons:

1. Stakeholders often don’t know what they want from a computer system except
in the most general terms; they may find it difficult to articulate what they want
the system to do; they may make unrealistic demands because they don’t know
what is and isn’t feasible.
2. Stakeholders in a system naturally express requirements in their own terms and
with implicit knowledge of their own work. Requirements engineers, without
experience in the customer’s domain, may not understand these requirements.
3. Different stakeholders have different requirements and they may express these
in different ways. Requirements engineers have to discover all potential sources
of requirements and discover commonalities and conflict.

4. Political factors may influence the requirements of a system. Managers may
demand specific system requirements because these will allow them to increase
their influence in the organization.
5. The economic and business environment in which the analysis takes place is
dynamic. It inevitably changes during the analysis process. The importance of
particular requirements may change. New requirements may emerge from new
stakeholders who were not originally consulted.

Inevitably, different stakeholders have different views on the importance and pri-
ority of requirements and, sometimes, these views are conflicting. During the
process, you should organize regular stakeholder negotiations so that compromises
can be reached. It is impossible to completely satisfy every stakeholder but if some
stakeholders feel that their views have not been properly considered then they may
deliberately attempt to undermine the RE process.
At the requirements specification stage, the requirements that have been elicited
so far are documented in such a way that they can be used to help with requirements
discovery. At this stage, an early version of the system requirements document may
be produced with missing sections and incomplete requirements. Alternatively, the
requirements may be documented in a completely different way (e.g., in a spread-
sheet or on cards). Writing requirements on cards can be very effective as these are
easy for stakeholders to handle, change, and organize.