The figure below shows the level 1 DFD, which is the decomposition (i.e. break down) of the system shown in the Context DFD. The Data Flow Diagram example contains three processes, two external entities and three data stores. Although there is no design guidelines that governs the positioning of shapes in a Data Flow Diagram, we tend to put the processes in the middle and data stores and external entities on the sides to make it easier to comprehend.
Based on the diagram, we know that the Perform Inspection process provides Bill to the Customer and store the Inspection result into the Inspection data store.
Posted by: Jason Voss