Relationship between the whole of software architecture and its parts: an NFR perspective

An interesting practical problem is the relationship of the non-functional requirements (or NFRs) of constituents of software architecture to the architecture. For example, if the constituents of a software architecture are adaptable (reliable, secure, usable, etc.), will the software architecture itself be adaptable (reliable, secure, usable, etc.)? It is generally accepted that the constituents of the software architecture are components, connections, constraints, styles and patterns. And, as a corollary, what is the minimum number of constituents that need to possess the NFR? This paper explores these problems for an industrial telecom system that is used as a case study and concentrates on a specific NFR, namely, adaptability. Employing the NFR framework for justification, this paper concludes that possession of the NFRs by the constituents is helpful for the final software architecture to possess that NFR. This paper also develops heuristics on how many constituents need to possess the NFR so that the final architecture possesses the NFR.