Data Flow Diagram

A "semi-formal" way of representing computer system functions in a diagram.

• represent major components or functions with Circles
• actions for input by a user or system go in Rectangular Boxes
• Databases are represented by parallel lines enclosing a phrase
• Display or output information is represented by a box with a truncated top right corner

from the Demurjian chapter on Software Design in Computer Science And Engineering Handbook - CRC Press

(he attributes Ghezzi, Jazayeri and Mandrioli Fundamentals of Software Engineering ) See http://www.infoarchgroup.com/qrdfd.htm for more description. Or, better, see TomDeMarco, Structured Analysis and Systems Specifications (Yourdon Inc., ISBN 0138543801 ).

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What is a DFD

Graphical Description of a System's data & how the process transform the data is known as Data Flow Diagram or simply DFD.

Unlike detail flowcharts, DFDs do not supply detailed descriptions of modules but graphically describe a system's data & how the data interact with the system.

To Construct a Data Flow Diagrams, we use:

• Arrows
  • Identifies data flow-data in motion. It is a pipeline through which information flows.
• Circles
  • Like the rectangle in flowcharts, Circles stand for a process that converts incoming data to information.
• Open-Ended Boxes or Parallel Lines
  • An Open-Ended box represents a data/store-data at rest, or a temporary repository of data.
• Squares.
  • A Square defines a source or destination of system data.

See http://www.infoarchgroup.com/qrdfd.htm

      Prepared By: Shiras Ahamed, Msc Computer Science, Calicut University Campus. 

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Actually, DFDs have broader application than just software. They can be used to describe business processes in a way that's a lot more readable than FlowCharts.

I have actually used a variation on this theme as a part of a job turnover project, wherein I had to describe everything I did and everything and everyone I touched. The DFD variant was the cleaner, more direct way of expressing this.

And, yes, I use them as an outline tool for software design.