"NFRs describe constraints on the solution space, and capture a broad spectrum of properties such as reliability, portability,maintainability, usability, safety, and security."
Ref.: Sommerville, I., and Sawyer, P., "Viewpoints: Principles, Problems, and a Practical Approach to Requirements Eng.,Annals of Software Eng., 3, N. Mead, ed., (1997), 101-130.
"Goal modeling primarily occurs during the elicitation, specification, and architectural design of the system. It is during this phase that non-functional goals are initially modeled as softgoals, decomposed into operationalizations, and negotiated and agreed upon between various stakeholders." (page 363)
Cleland-Huang, J., Settimi, R., BenKhadra, O., Berezhanskaya, E., Christina, S. Goal-Centric Traceability for Managing Non-Functional Requirements.ICSE’05, May 15–21, 2005, St. Louis, Missouri, USA. Copyright 2004 ACM.
This was just a fast copy/paste to start somewhere. Additions, corrections, comments are appreciated to continue the discussion.
--merja bauters, 18-Mar-2007