Internet-of-Things Architecture © - 259 -
As one can see, this requirement is indeed a constraint in that it tells the
architecture not to include payement transations in the architecture, something
that is tacitly covered in the IoT Context View (see above), but in order to avoid
slips during the architecting process, it is often very helpful not only to state
what is within the system scope but also what is outside of the system scope.
An example for a design constraint at the reference-architecture level is
UNI.071, viz. ―A system built using the ARM shall provide standardised and
semantic communication between services‖. Here, it is emphasised to
standardise interfaces. In other words, non-standardised interfaces do not lie
within the scope of the architecture.
Qualitative requirements
As discussed above and in Sections 4.3, qualitative have impacts on more than
one view. What is not mentioned in these sections though, is that qualitative
requirements can inform the same architectural design decision. In order to
elucidate this point let us look at the three qualitative requirements that inform
the decision to store the Parking White List in a Virtual Entity Repository instead
of Virtual Entity Resolution FC. These requirements are listed below.