A data flow diagram (DFD) depicts the flow of data in any system or process. It shows data inputs, outputs, storage sites, and paths between each destination using predetermined symbols such rectangles, circles, and arrows, together with short text descriptors.
Data flowcharts can range from simple, even hand-drawn process overviews to in-depth, multi-level DFDs that go deeper into the data handling process. They can be used to analyse or model an existing system. A DFD, like all the best diagrams and charts, can frequently graphically 'express' things that are difficult to convey in words, and they may be used by both technical and nontechnical audiences, ranging from developers to CEOs.
That is why DFDs have remained so popular over the years. While they are useful for displaying data flow software and systems, they are less useful for interactive, real-time, or database-oriented
software and systems nowadays.