A Prescriptive Approach to Quality-Focused System Architecture

The most critical requirements for the lifetime value of a system are its nonfunctional requirements (NFRs) such as reliability, security, maintainability, changeability, etc. These are collectively known as the “ilities,” and they are typically not addressed in system design until the functional architecture has been completed. In this paper, we propose the use of quality-based design that modifies this standard process so that those NFRs, which actually reflect the true business needs, are addressed first. This is accomplished through a combination of quality attribute workshops, to elicit and refine quality-based mission objectives, and attribute-driven design, where design heuristics, termed tactics, can be employed in the decomposition of the system. This ensures that the final system better reflects and embodies those architecturally significant requirements rather than having them addressed secondarily. This is an important change since the “ilities” are systemic properties (properties of the system as a whole) rather than properties of individual components or subsystems. Consequently, they are difficult to address in an architecture that has already been decomposed with respect to required functionality. To illustrate the proposed approach, we provide an example based upon the Department of Defense Pre-positioned Expeditionary Assistance Kit.