Using the containment relationship the requirement
would have the qualified name Essential requirements::Convenience functions::Radio. This
problem is a current issue of the SysML working group.
44 CHAPTER 2 The Pragmatic SYSMOD Approach
requirement is not needed without the comfort functions requirement. It is existentially
contained in the requirement. You can see the result in Figure 2.10 . This
fi gure already gives a hint to an important fact that further modeling will confi rm:
If our contractor eventually decides to do without the comfort functions, then
this will have only a minor effect on the core function, namely picking up and
returning a car. There is an enormous cost savings potential in this fact.
The separation of essential from technical requirements corresponds to the
differentiation between user specifi cation and system specifi cation. A user specifi -
cation contains the principal ??™ s requirements from the user perspective. A system
specifi cation is prepared by the contractor. It contains details about the requirements
from the user specifi cation, further enhanced by requirements that refer to
concrete solution approaches [10].
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