For example : Customer --->(customer details) SEND DETAILS --->(customer details) --->Clerk
Typical Dataflow diagrams (DFD) represent distinct flow of data between two functions as a distinct edge, regardless of the type of data:
+----------+ +--------------+ +-------+ | Customer |---Customer details--->| SEND DETAILS |---Customer details--->| Clerk | +----------+ +--------------+ +-------+
The graphical notation may vary slightly between Yourdon/DeMarco and Gane&Sarson, but the principle stays the same.
In the more modern UML notation, there is a very similar information flow diagram. Alternatively, you may also use an UML activity diagram. It is more general as a DFD, because it shows the flow of activities, and not only flow of data. But data flow can be made explicit therein with object nodes and pins.
Some diagramming methods look like DFD but have a different purpose, and a different meaning:
- IDEF0 may regroup one kind of data on a single arrow with branches to and back to process that may alter the flow. But these diagram represent the functional decomposition of a process: they are not meant to represent sources and addressees/stores (i.e. no customer, and no clerk).
- UML sequence diagram represent each instance of objets (data+ their behavior) only once, with a lifeline. The arrows are messages exchanged, which have a very different semantic from a simple data flow.
So in some diagramming methods, same data used in different places would be represented only once. But in your DFD, you don't have to take care about such data identity or redundancy.