Data flow diagram is usually used to show model the system’s data processing. All the processing steps are shown in the diagram through the system. They are the intrinsic part of the many analysis or design methods. They are modeled to show how the data flow through the system, how the data are flown in the system and how are they related to each other. They also depict how the data are stored at the specific locations in the system. This diagram helps showing how the data are transformed in the system.
Simple and intuitive notations are used for easy understanding showing the end-to-end processing of data. Notations used in this model represents the functional processing (represented by the rounded rectangle), data store (represented by the rectangle )and the data movement between the functions (represented via labeled arrows).
The symbols to define the DFD symbols are given in the given figure:
Generally the data flow models are not supported by the UML as they were supposed to model the data. The reason behind this thing is that the DFDs focuses on the system functions and does not recognize the system objects.
During the software development process one has to be very careful with their data and their flow in the system. One has to be totally concerned about the data rather than the UI. The data flow within the system must be pre-defined as it is the most important part of the system. Logically it shows the clear view of the data that is exchanged by our system processes and external interfaces, but it does not show when and what information is exchanged. These all flow of data can be represented graphically clearly showing the path way for the data flow, and this diagram is called the data flow diagram (usually abbreviated as DFD). It is one of the important and essential perspective of the structured system analysis and design methods which has much more use than the recent object oriented design methods. Any business analysts must use the DFD while reviewing the original documentation.
This type of diagrams are based in the Gane-Sarson Symbol set. Although being more concerned about the computer system, this diagram has a large aspect in the non-computerized systems too. Basically, we have 4 types of shapes used in the DFD.
Process: It is Lozenge shape, consuming the data from an interface or the data store.
Interface: It is rectangle in shape which is any external systems or the actor that interacts with the system.
Data Store: This represents a entire databases which is rectangle in shape with one side open.
Data Flow: It shows the flow of the data from a process to the external interface or the data store. Can be in any direction.