This characteristic represents the degree to which a product or system provides functions that meet stated and implied needs when used under specified conditions. This characteristic is composed of the following sub-characteristics:
- Functional completeness - Degree to which the set of functions covers all the specified tasks and intended users' objectives.
- Functional correctness - Degree to which a product or system provides accurate results when used by intended users.
- Functional appropriateness - Degree to which the functions facilitate the accomplishment of specified tasks and objectives.