It is at this point, that the diagram ceases being a functional decomposition and instead becomes a process decompostion. It is important at this time to differentiate between a function and a process. A function is a set of business activities that does not have a finite start and end point. The function is generally an ongoing effort within in a company. A process is a business activity which does have a finite start and end point.
Processes are generally a lower level of abstraction than a process.
Accounts Payable is a function and Create a Check is a process. A functional decomposition diagram was useful in an information engineering environment. The functions were decomposed to processes. The processes were converted to program specifications. The program specifications were converted to program code.