Process – An activity that changes or transforms data flows. They can represent another system or indicate a subsystem. Since they are external to the system being analyzed, these entities are typically placed at the boundaries of the diagram. These data flows are the inputs and outputs of the DFD. If you’re using DFD software, it will likely dictate which set of symbols are available to use.Īll data flow diagrams include four main elements: entity, process, data store and data flow.Įxternal Entity – Also known as actors, sources or sinks, and terminators, external entities produce and consume data that flows between the entity and the system being diagrammed. Because DFD symbols vary, it’s important to be consistent with whatever notation you choose in order to avoid confusion. Another variation is the symbol used for data stores-Yourdon and Coad uses parallel lines while Gane and Sarson notation uses an open-ended rectangle. For example, Yourdon and Coad notation uses circles to represent processes, whereas Gane and Sarson notation use rectangles with rounded corners. There are some differences in style between the notation types. The two main types of notation used for data flow diagrams are Yourdon-Coad and Gane-Sarson, both named after their creators, all experts who helped develop DFD methodology: Ed Yourdon, Peter Coad, Chris Gane and Trish Sarson.
