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It is usually beginning with a context diagram as level 0 of the DFD diagram, a simple representation of the whole system. It may be used as a communications tool between a systems analyst and any person who plays a part in the system that acts as the starting point for redesigning a system. The purpose of a DFD is to show the scope and boundaries of a system as a whole. It shows how information enters and leaves the system, what changes the information and where information is stored. It can be manual, automated, or a combination of both. A neat and clear DFD can depict a good amount of the system requirements graphically.
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A Data Flow Diagram (DFD) is a traditional way to visualize the information flows within a system.
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