Data-flow models are an intuitive way of showing how data is processed by a system. At the analysis level, they should be used to model the way in which data is processed in the existing system. The use of data-flow models for analysis became widespread after the publication of DeMarco’s BOOK on structured systems analysis. They are an intrinsic part of structured methods that have been developed from this work. The notation used in these models represents functional processing (rounded rectangles), data stores (rectangles) and data movements between functions (labelled arrows).
Figure 1 shows a data-flow diagram for equipment procurement. This illustrates the processing steps with the area bounded by dotted lines, showing the boundaries of the system to be implemented.