As shown below, the System Data Flow diagram depicts all processes within the information system, a focus that results in a very detailed model. The model is comprised of various symbols. The square symbols represent the “external agents,” who should be thought of as those people or parties interacting with the information system. The interaction of these agents with the system is handled by various processes or functions, as represented by the symbol comprised of the rounded double rectangles. Frequently these process/function symbols will cross-reference to a Decomposition Diagram. These processes rely on inputs from either the system’s external agents or “data stores,” which are depicted with the open-ended rectangles. The processes produce outputs that are either added to data stores or presented to external agents. Both inputs and outputs are symbolized with the arrowed lines. With smaller information systems projects, a detailed diagram of this sort may not be required. However, this does not mean that a clear understanding of the processes can be avoided by key stakeholders during the analysis phases of the project. As with both the Context Data Flow Diagram and the Decomposition Diagram, the System Data Flow Diagram is meant to show what the system will achieve. The technical consideration for how the system will achieve these functions is reserved for the physical design phase.

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Since the System Data Flow Diagram (above) covers the entire system, some processes and functions may need to be summarized. Therefore, additional, more detailed diagrams, known as Primitive Data Flow Diagrams, may be created to show in more detail how these more complex processes work.