2.3 Functional Area Sections
Once we’ve written all our introductory and contextual material, we’re left with the task of specifying the guts of the system. So how should we organize the main body of the specification? It is convenient to divide it into a number of sections to make it more manageable and easier to understand.
Functional areas are the best way of organizing the main body of the specification—which means writing a top-level section for each logical grouping of functions, usually based on the primary interest of each type of user. In short, write a section for each major actor.
Name each section for its functional area: “Customer Functions,” “Customer Service Functions,” “Accounting Functions,” and so on. Use the language your customer uses for these areas. It doesn’t matter how many functional area sections you end up with: there may be one or twelve—both are fine. Create the sections you need, and let everything else take care of itself.
Order these sections according to their importance (from highest to lowest), though what constitutes important varies from system to system. It could mean the frequency of use of the functions in each area, the intrinsic relative importance of the actors, or the value, in some other way, to the business. Typically, however, the functional area in which business originates is the most important, followed by other areas, according to the length of time it takes new business to flow through to them.