Data Flow Diagram (DFD) display how data moves in a very System and where it’s stored. There is actually four symbol regarding DFD those tend to be Process, External thing, Data flow and Data store. The actual large rectangular field represent data dealing with process. This practice takes inputs, then process and changes the data and finally productivity it to somewhere else. The oval shap signify external entities. External entities are the things which are outside the machine but any how related to the system. When a External entities occurs twice from the diagram and features a slash in the top left hand corner of the oval.