Writing a functional requirements document (frd) is an essential step in the software development process. The frd is produced by business analysts or sometimes the technical team in response to the business. The overall obs covers a wide range of features, which are. A functional specification document (fsd), also known as a functional requirements document (frd), is considered by many project management and software. [provide a list of contractual or task level assumptions and/or constraints that are preconditions to preparation of the frd.