An NFR Pattern Approach to Dealing with NFRs

Non-functional requirements (NFRs), such as security and cost, are generally subjective and oftentimes synergistic or conflicting with each other. Properly dealing with such NFRs requires a large body of knowledge-goals to be achieved, problems or obstacles to be avoided, alternative solutions to mitigate the problems, and the best compromising alternative solution to be selected. However, few patterns exist for dealing with these kinds of knowledge of NFRs. In this paper, we present four kinds of NFR patterns for capturing and reusing knowledge of NFRs-objective pattern, problem pattern, alternatives pattern and selection pattern. NFR patterns may be visually represented, and organized by rules of specialization to create more specific patterns, of composition to build larger patterns, and of instantiation to create new patterns using existing patterns as templates. We have applied the NFR pattern approach to the TJX incident, one of the largest credit card theft in history, as a realistic case study.