Data flow diagram

A data flow diagram (DFD) is graphic representation of the flow of data through business functions or processes. More generally, a data flow diagram is used for the visualization of data processing. It illustrates the processes, data stores, and external entities in a business or other system and the data flows between these things. Physical DFD s represent physical files and transactions, or while logical or conceptual DFD s can be used to represent business functions or processes. DFDs can be of an existing system, or can describe the requirements for a proposed or planned system. A DFD of an existing system should represent the functions and processes that are already in place, flaws and all. A required system DFD is a diagram of a system that will be implemented in the place of the current one. Data flow diagrams were invented by Larry Constantine, the original developer of structured design, based on Martin and Estrin s data flow graph model of computation.

=Components=

The components described or illustrated in a DFD should include:

=External Entities=

A data flow diagram s boundary is the imaginary boundary of the system. This is conventionally drawn on the diagram as a continuous line going through all the data flows from external entities to processes and back.

Note: It is a bad practice to have external entities have direct access to data stores.

External entities and data stores can be duplicated in the system for more clarity, while processes cannot. External entities that have been replicated are marked by * in the lower right part of the oval that represents that entity. Data stores have a double line of the left side of their box.

=External links=

*[http://infoarchgroup.com/qrdfd.htm Quick Reference] *Article [http://www.umsl.edu/~sauter/analysis/dfd/dfd_intro.html Data Flow Diagrams (DFD)] by Vicki L. Sauter *Article [http://www.cems.uwe.ac.uk/~tdrewry/dfds.htm Data Flow Diagrams] by Tony Drewry *Article [http://spot.colorado.edu/~kozar/DFD.html Representing Systems With Data Flow Diagrams] by Kenneth A. Kozar *Article [http://citeseer.ist.psu.edu/271116.html The Semantics of Data Flow Diagrams] by P. D. Bruza and Th. P. van der Weide *Chapter [http://www.yourdon.com/strucanalysis/chapters/ch9.html Dataflow Diagrams] by Ed Yourdon