Nelson Souto Rosa,  Paulo Cunha. 

Non-functional requirements (NFRs) are rarely taken in account in most software development processes. There are some reasons that can help us to understand why these requirements are not explicitly dealt with: their complexity, NRFs are usually stated only informally, their high abstraction level and the rare support of languages, methodologies and tools. In this paper, we concentrate on defining how to reason and how to refine NRFs during the software development. Our approach is based on software architecture principles that guide the definition of the proposed refinement rules. In order to illustrate our approach, we adopt it to an appointment system.

http://www.lbd.dcc.ufmg.br/colecoes/jbcs/10/1/006.pdf

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