A data flow diagram is a graphic representation of a system or portion of system. It consists of data flows, processes, sources, destinations, and stores - all described through the use of easily understood symbols. An entire system can be described from the viewpoint of the data it processes with only four symbol. At the same time, data flow diagrams are powerful enough to show parallel activities. When standard symbols limit communication, a presentation graph, which uses symbols of people, files, terminals, and documents, can be used to discuss a system with users. Which kind of data flow diagrams would a particular (manufacturing, retail, non-profit) business use, for what purpose and why?