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Data Flow Diagram

A Data Flow Diagram, or DFD, is used to display the flow of data in an information system. There are 2 types of notation used in a DFD: Yourdon & Coad or Gane & Sarson. They differ in the types of shapes used to describe a process and data store. A data flow diagram includes four components: terminators/external entities, processes, data stores, data flows.

Data Flow Diagram
Typical Uses

A DFD is most useful when it is necessary to document the flow of data within a currently used system, or a system that is in the process of being built. Data flow diagrams are helpful for both software engineers and operations personnel because their creation does not require technical knowledge.

Best Practices
  • Identify the process. Define the start and end point for the process to be examined.
  • Add a process. Once the starting point has been established, add a process. In a DFD, processes are represented by circles with labels in the center. Draw the circle spaced slightly apart from the start point.
  • Draw a flow line. Connect the start point and first process with a solid line ending in an arrowhead. The arrowhead should point from the start point toward the first the process, indicating the direction in which the information is flowing.
  • Repeat. Continue to add processes and data flow lines until all of the systems processes have been added. When adding data flow lines, start the line at the process that is sending information out, and end the line with the process that is receiving the information.
  • Datastores & files. Some processes produce files (such as a Word document) or store information. These are called data stores, places in which information is remembered, so that it can be accessed by others at different times. They are noted by two horizontal & parallel lines. When a process leads to a file, add a data store along the data flow line between two processes.
  • Verify accuracy. Consult with all stakeholders to verify accuracy.

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