  Requirements are often divided into functional requirements (FRs) and quality
requirements (QRs). However, we still have little knowledge about to which
extent this distinction makes sense from a practical perspective. In this
paper, we report on a survey we conducted with 103 practitioners to explore
whether and, if so, why they handle requirements labeled as FRs differently
from those labeled as QRs. We additionally asked for consequences of this
distinction w.r.t. the development process. Our results indicate that the
development process for requirements of the two classes strongly differs (e.g.,
in testing). We identified a number of reasons why practitioners do (or do not)
distinguish between QRs and FRs in their documentation and we analyzed both
problems and benefits that arise from that. We found, for instance, that many
reasons are based on expectations rather than on evidence. Those expectations
are, in fact, not reflected in specific negative or positive consequences per
se. It therefore seems more important that the decision whether to make an
explicit distinction or not should be made consciously such that people are
also aware of the risks that this distinction bears so that they may take
appropriate countermeasures.
