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112 Chapter 4 Requirements engineering

Enduring and volatile requirements

Some requirements are more susceptible to change than others. Enduring requirements are the requirements that
are associated with the core, slow-to-change activities of an organization. Enduring requirements are associated
with fundamental work activities. Volatile requirements are more likely to change. They are usually associated with
supporting activities that reflect how the organization does its work rather than the work itself.
http://www.SoftwareEngineering-9.com/Web/Requirements/EnduringReq.html

Once a system has been installed and is regularly used, new requirements inevitably
emerge. It is hard for users and system customers to anticipate what effects the new
system will have on their business processes and the way that work is done. Once end-
users have experience of a system, they will discover new needs and priorities. There
are several reasons why change is inevitable:
1. The business and technical environment of the system always changes after
installation. New hardware may be introduced, it may be necessary to interface
the system with other systems, business priorities may change (with consequent
changes in the system support required), and new legislation and regulations
may be introduced that the system must necessarily abide by.

2. The people who pay for a system and the users of that system are rarely the
same people. System customers impose requirements because of organizational
and budgetary constraints. These may conflict with end-user requirements and,
after delivery, new features may have to be added for user support if the system
is to meet its goals.
3. Large systems usually have a diverse user community, with many users having
different requirements and priorities that may be conflicting or contradictory.
The final system requirements are inevitably a compromise between them and,
with experience, it is often discovered that the balance of support given to differ-
ent users has to be changed.
Requirements management is the process of understanding and controlling
changes to system requirements. You need to keep track of individual requirements
and maintain links between dependent requirements so that you can assess the
impact of requirements changes. You need to establish a formal process for making
change proposals and linking these to system requirements. The formal process of
requirements management should start as soon as a draft version of the requirements
document is available. However, you should start planning how to manage changing
requirements during the requirements elicitation process.

4.7.1 Requirements management planning
Planning is an essential first stage in the requirements management process. The
planning stage establishes the level of requirements management detail that is
required. During the requirements management stage, you have to decide on: