Software quality is commonly described in terms of what are known as non-functional requirements. An NFR is a quality of a software system that will be adjudged directly by stakeholders. Quality attributes are quantifiable by appropriate and practical scales of measure. To be effective, NFRs need to be, not only defined, but also approved and enforced. The following diagram depicts the four different approaches to NFR measurement.

The key topics covered in this chapter related to NFRs are:

• Measuring and monitoring
• Sizing
• Analytical modeling
• Quality Assurance