Definition of the term („What is a functional specification?“) 

A func­tio­n­al spe­ci­fi­ca­ti­on con­tains a contractor’s de­tail­ed de­scrip­ti­on how he in­tends to sol­ve the cus­to­mers re­qui­re­ments. As the pre­ce­ding in­stance, howe­ver, the con­trac­ting en­ti­ty must de­fi­ne the user re­qui­re­ment spe­ci­fi­ca­ti­on as de­tail­ed as pos­si­ble in a func­tio­n­al spe­ci­fi­ca­ti­on. This way, it is ad­vi­s­able that the con­trac­ting en­ti­ty first ac­cepts the func­tio­n­al spe­ci­fi­ca­ti­on be­fo­re the con­trac­tor be­gins with the implementation.

Fur­ther­mo­re, it is com­mon prac­ti­ce to ap­p­ly the in­clu­si­on and ex­clu­si­on princip­le when crea­ting a re­qui­re­ment spe­ci­fi­ca­ti­on to ex­pli­ci­tly igno­re or in­clu­de spe­ci­fic ca­ses. With re­fe­rence to soft­ware de­ve­lo­p­ment, the func­tio­n­al spe­ci­fi­ca­ti­on is also de­fi­ned as part of the V model.