A functional specification is a type of specification which defines what the product or service has to be able to do. Together with performance specifications, functional specifications are output specifications, as the focus is on what the solution needs to do, rather than how the solution should be designed, which would be an input or detailed specification. For example, a functional specification for a kettle might read ‘design a portable system which can boil water’. Functional specifications encourage suppliers to show innovation, though evaluation of alternative solutions may be more difficult as we may not be comparing ‘apples with apples’. See also Specification.