Functional specification (FS)

A document, usually written by the supplier, that describes in technical terms how a system will meet each user requirement: functions, operating ranges, alarms, interfaces and data handling. In the V-model it is verified during operational qualification. A traceability matrix links each user requirement to the functional specification and to the test that verifies it. Gaps or mismatches between the user requirement specification and the functional specification tend to surface late, during qualification or supplier acceptance testing, so review the two documents together.