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Broadly, functional requirements define what a system is supposed to do and non-functional requirements define how a system is supposed to be mathematical function, a black box description input, output, process and control functional model or IPO Model.roadly, functional requirements define what a system is supposed to do and non-functional requirements define how a system is supposed to be mathematical function, a black box description input, output, process and control functional model or IPO Model.
Non-functional requirements cover all the remaining requirements which are not covered by the functional requirements. They specify criteria that judge the operation of a system, rather than specific behaviours, for example: âModified data in a database should be updated for all users accessing it within 2 seconds.â.