Sommerville-Software-Engineering-10ed

132 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://software-engineering-book.com/web/changing-requirements/
process. Rather, the user has to prioritize that change and, if it is high priority, decide
what system features that were planned for the next iteration should be dropped for
the change to be implemented.
The problem with this approach is that users are not necessarily the best people to
decide on whether or not a requirements change is cost-effective. In systems with
multiple stakeholders, changes will benefit some stakeholders and not others. It is
often better for an independent authority, who can balance the needs of all stakeholders,
to decide on the changes that should be accepted.
4.6.1 Requirements management planning
Requirements management planning is concerned with establishing how a set of
evolving requirements will be managed. During the planning stage, you have to
decide on a number of issues:
1. Requirements identification Each requirement must be uniquely identified so
that it can be cross-referenced with other requirements and used in traceability
assessments.
2. A change management process This is the set of activities that assess the impact
and cost of changes. I discuss this process in more detail in the following section.
3. Traceability policies These policies define the relationships between each requirement
and between the requirements and the system design that should be recorded.
The traceability policy should also define how these records should be maintained.
4. Tool support Requirements management involves the processing of large
amounts of information about the requirements. Tools that may be used range
from specialist requirements management systems to shared spreadsheets and
simple database systems.
Requirements management needs automated support, and the software tools for
this should be chosen during the planning phase. You need tool support for:
1. Requirements storage The requirements should be maintained in a secure, managed
data store that is accessible to everyone involved in the requirements engineering
process.