Functional requirements, non-functional requirements, and architecture should not be separated -A position paper

Requirements engineering approaches have for a long time mainly focused on functional requirements . During the last 5 years, several approaches dealing specifically with non-functional requirements have emerged. They support the elicitation, documentation, verification and validation of nonfunctional requirements: sometimes only concentrating on the non-functional requirements, sometimes in conjunction with functional requirements, and sometimes in conjunction with architecture. The position we put forward in this paper is that functional requirements, non-functional requirements, and architecture must be treated together. It is well known that functional requirements (FRs) and non-functional requirements (NFRs) constrain each other and therefore should be treated together. Similarly, it is well known that both FRs and NFRs must be realized through the architecture. However, typically, the development of an architecture is not considered part of requirements engineering. In this paper we argue that FRs, NFRs and architectural decisions (ADs) must be developed in a tightly integrated approach. In the rest of the paper, we first sketch the solutions published so far that deal with NFRs and FRs or ADs. Then, we motivate our case with an example. We argue that none of the existing approaches has truly addressed all three issues in a coherent and integrated manner. Finally, we discuss the most critical research questions that result from considering such an integrated approach.