5. Specify Non-Functional Requirements. Non functional requirements are constraints on the
system design. They may arise from user requirements, technical disciplines or the external
environment. They are often "ilities", can be divided into product or support constraints and
include the following areas:
Non-functional requirements are often expensive but add quality. Early identification will avoid
costly changes and facilitate the trade-off process leading to a cost-effective solution. Blanket
application of individual non-functional requirements will be unnecessarily costly and should be
avoided. They should be identified against and linked to the lowest level function in the
decomposition to which they specifically apply. Non-functional requirements should also be
expressed as unique statements of requirement with the same attributes as system functions.