A data flow diagram (DFD) graphically described the flow of data within an organization. It is used to document existing system and to plan and design new ones. There is no one ideal way to develop a DFD: different problems call for different methods.
A DFD is composed of four basic elements: data sources and destination, data flows transformation processes, and data stores, and data stores. Each is represented on a DFD by one of the symbols shown in figure 2.
These four symbols are combined to show how data are processed. For example, the DFD in Figure 3 shows that the input to process C is data flow B, which comes from data source A. The output of process C are data flows D and E. Data flow E is sent to data destination J. process F uses data flows D and G as input and produces data flow I and G as output . Data flow G comes from and returns to data store H. Data flow I is sent to data destination K.