Data Flow Diagram (DFD): DFD graphically describes the flow of data within an organization. It is used to document existing systems and to plan and design new ones. DFDs are subdivided into successively lower levels in order to provide ever-increasing amounts of detail, because few
systems can be fully diagrammed on one sheet of paper. Since users have differing need at variety of levels can better satisfy these requirements.The highest-level DFD is referred to as a context diagram. A context diagram provides the reader with a summary-level view of a system. It depicts a data processing system as well as the external entities that are the sources and destinations of the system‘ inputs and outputs.