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4.2.1 Data Flow Diagram Example

Figure 7 shows the top-level DFD for the Commanding function. This DFD was generated based on an analysis of commanding requirements in the SSCS FRD. The DFD graphically depicts the overall structure and relationships between the key functional components of the Commanding application.

Figure 7. Overall Commanding data flow diagram.

A DFD identifies functional components and indicates the data that flows between those functional components. Ovals represent functions included in SSCS. Rectangles represent sources or sinks which portray components that are external to our architecture. These DFDs also show any needed data stores, which could consist of flat files, databases, and/or knowledge bases. These data stores are indicated by parallel lines surrounding the data store name.

A distinction is made between functions internal to Commanding and those external to Commanding. Ovals with thin lines are internal to the subject application (e.g., Commanding) and ovals with thick lines represent applications external to the subject application, but internal to SSCS. Functions and data stores that are mission-specific are indicated by shading.

Several subfunctions of Commanding have been broken down into complete flow diagrams in Appendix C. Certain functions require descending to three levels of DFDs to completely represent the functionality.

While this flow indicates functions and flow of data through those functions, it does not provide timing information. For example, looking at the DFD, one would not know if these functions are performed in parallel, in series, or some combination. Such timing information is provided in a CFD.