A nonfunctional requirement is a quality or property that the product must have. Sometimes this type of requirement is critical to the product's success, but often it simply enhances the product's looks or identifies the product as something unique to the organization. Nonetheless, it is a requirement, and it is important to the customer—sometimes even more important than a functional requirement. An example of a nonfunctional requirement statement is:
The Essex Company logo will be prominently displayed on the front of the product.
This requirement, the company's logo, clearly doesn't affect the functionality of the product. The product will work regardless of whether the logo is present. But to the Essex Company, this logo prominence may be of significant marketing importance, particularly if the product is critical to an operation and its contribution is seen by hundreds of people. Consider, for example, the timing equipment used at the Olympics. As important as the accuracy and reliability of the equipment is, it is just as important, to the provider at least, that the company name be prominently displayed on or with the equipment.
Nonfunctional requirements are often overlooked during the requirements identification process or, if not overlooked, they are considered less important and not given the appropriate attention. This negligence can be catastrophic. Consider the following story.
Several years ago, an elderly woman living in an old Boston mansion decided to sell her house and move to another state to be near her children. The woman, a widow, had lived in the house nearly her entire life. The house was built around the turn of the century by her parents; she grew up in the house, inherited it from her parents, and raised her own family there. But as she aged, she wanted to be near her two children, both of whom lived and worked in Florida. The house went on the market, but the woman rejected every offer, even several that exceeded her $3,000,000 asking price. She finally accepted an offer from a young couple for a little over $2,000,000. When asked why she rejected every offer but this particular one, and for nearly $1,000,000 less than the asking price, she explained her reason. "Every person who made me an offer had grand plans for either changing the house or for demolishing it altogether to make room for a completely new house. The man who offered me the most money even planned to subdivide the property and build several nice but smaller homes. I didn't want to see the house I was born in and lived in my entire life destroyed. The young couple that bought the house told me they didn't have the price I asked, but they loved the house so much they wanted it so they could eventually restore it to its original condition. Furthermore, they promised me that they would not change my bedroom for as long as I live, but would leave it as is for me to visit and use anytime."
This story is not about requirements in the sense that we are considering project descriptions, but it demonstrates an important point. What the customer really wants may not be obvious. Her real interests may be nonfunctional. In the example of the woman and her house, the primary requirement was selling the house so she could move to Florida. But the woman's overriding desire was that the house be preserved in the way that she had cherished it. The moral of this story is that we must be careful to identify and interpret all of the customer's requirements.