A graphical depiction of the relationships among and between the various components and processes in a program or system. They depict how input data is transformed to output results through a sequence of functional transformations and consist of four major components - entities, processes, data stores, and data flows.
A DFD can be either logical or physical. A logical DFD focuses on the business processes surrounding the data flow. A physical DFD focuses on the implementation of the data flow and includes manual process details and data structures.