Software Engineering

10.4.5 
Functional specifications
A specification must be developed for each functional component and unit. These 
specifications provide the traceability among elements in the functional hierarchy 
to the specified software requirements. The functional unit specifications are uti-
lized during software design synthesis to establish structural unit specification 
(see Chapter 13). A fundamental principle of engineering is the specification of every 
part or component involved in the design of the product. Functional specifications 
are also necessary to support software reusability. The selection of reusable software 
components is predicated on how well a commercially available (commercial off the 
shelf, COTS) or previously developed (nondevelopmental item, NDI) software com-
ponent satisfies the required functionality and performance.