A data flow diagram is one of the many diagramming tools in the systems analyst's toolbox. For a quick overview of DFDs, connect to the Applied Information Science site at www.aisintl.com/case/dfd.html. DFDs were suggested as early as 1977 in the now classic text, Structured Systems Analysis by Gane and Sarson (Prentice-Hall, 1977). An alternative approach using a slightly different symbol set was proposed by Tom De Marco in Structured Analysis and Systems Specifications (Yourdon, Inc., 1979).You'll find a sample set of DFDs at Professor Sauter's site, www.umsl.edu/~sauter/analysis/dfd/dfd.htm.