"A requirement states the least stringent condition that must hold to solve or avoid a problem that a prospective customer faces."Assume we are developing a temperature control system, and the problems that prospective customers face include:
- Prospective customers feel too cold or too hot in their homes.
- Prospective customers will feel frustrated if it takes more than one minute of their time per day to maintain a comfortable temperature.
Here are two possible ease of use constraints:
a. The system will be a thermostat with a dial to set the desired temperature, a switch that determines cooling or heating mode, and an on/off switch.It is conceivable that we could solve problem 2 with a temperature control system that did not have the user interface specified in constraint 'a'. Therefore, ease of use constraint 'a' is not a requirement, as it is not the least stringent condition that must hold to solve problem 2.
b. For a user that fits profile 'x', it should take no longer one minute of his time per day to maintain a comfortable temperature in his home.
Constraint 'b', on the other hand, flatly restates the prospect problem in terms of a negative condition. It is therefore a requirement.