Creating Data Flow Diagrams

The two main styles of data flow diagrams are the 1) Yourdon/DeMarco style and 2) the Gane and Sarson style. The Yourdon/DeMarco uses squares, circles, and parallel lines to represent data handlers, processes, and databases, respectively. The Gane & Sarson style, on the other hand, uses squares, round-cornered rectangles, and open-ended rectangles to represent data handlers, processes, and databases, respectively.
CASE tools are useful for creating data flow diagrams, just as they are useful for creating ER diagrams. While different CASE tools use slightly different symbols in their diagrams, the diagrams illustrate the same information and are interpreted in the same manner.

A data flow diagram (DFD) is a graphical representation of the "flow" of data through an information system, modeling its process aspects. Data flow diagrams are a preliminary step used to create an overview of the system which can later be elaborated.DFDs can also be used for the visualization of data processing (structured design). A DFD shows the kind of information that will be input to and output from the system. A DFD shows the input and output of a system.It does not show information about the timing of processes, or information about whether processes will operate in sequence or in parallel .