Nonfunctional Requirements

Nonfunctional requirements are the properties that the product must have. In this section you describe what the spirit of the product's appearance is, how easy it must be to use, how secure it must be, what laws apply to the product, and anything else that must be built into the product, but is not a part of its fundamental functionality.

Nonfunctional requirements are written like other requirements. That is, they have all the usual componentsthey are identified, they have a type, they have a description, they have a fit criterion, and so on. Thus you write them just as you would a functional requirement (see Figure 10.7).

Figure 10.7.

A nonfunctional requirement.

See Chapter 9, Fit Criteria, for details on how to quantify nonfunctional requirements.