Abbreviated as DFD, data flow diagram is a technique used in the early phase of a business process re-engineering to visualize and study the flow of information and data between the business processes. It is used to define the structure of "Data processing" in a system, in terms of inputs and outputs.
The basic purpose of using a DFD is to define and create a general overview of a system before detailing it, for the purpose of designing and structuring the system. In addition, it is used to identify the points from where the data of a certain type may be fed to a system, where it may move or flow, and where it may be stored irrespective of timing of a process.
Basically, four symbols or notations are used to create a DFD, which may be seen as under:
Represented by a circle shape, process or function element in a DFD is used to receive the input data flow and accordingly decides and directs the data's output flow, i.e. it transforms the input data flow in output data flow.
It is used to depict the movement or flow of the data in the system.
Depicted by two parallel bars, data store element imparts the data repositories, which shows the data in a buffer or in a queue for the purpose of processing.
These are the external elements outside the system's boundaries, with whom, the system interacts and communicates. They are used to represent the sources for the input data and the destination for the output data.
In the context level DFD, we only see an overall system, namely "Book Ordering System" interacting/communicating, with three external entities-customer and Vendors/Retailers.
Here, we divide the overall book ordering system into its sub-systems or sub-modules to perceive the flow of data between the processes along with the external entities.
Similarly, for Level-2 DFD, we may further divide the sub-modules of a system into their sub-systems to view the data flow among them. For example payment gateway module may be further divided into its sub-modules namely, Credit/Debit Card payment option, Net Banking option, Cash on Delivery option, to view the flow of data between them.
Below, given are some of the merits of using a DFD.