- A data flow diagram (DFD) is a graphic representation of the application's component parts.
- The entities and data flows from the context diagram are all present ini DFD.
- Data flows may connect processes to other processes, data stores, or external entities.
- Data stores and external entities do not interact directly with each other.
- All entities and data flows from the higher level processes must be in every more detailed diagram. The names of entities and data flows must be consistent across the levels of the diagrams
DFD Rules:
- Define the processes.
- Define the files and other data flows required to support the processes.
- Draw a Level 0 DFD. At level 0, ignore trivial error paths and data stores. If you define a validation process, you must eventually identify an error path. Define the error path at the primitive level. Similarly for data stores, define files when they are shared between processes. Introduce files that are only used within a given process at the level at which the file is shared between two or more subprocesses.
- Balance the DFD with the context diagram. Compare the net inputs and outputs to external entities on the DFD to the net inputs and outputs on the context diagram. There should be a one-to-one correspondence between the diagrams.
- Iterate through this procedure until the primi-tive level of DFD is reached for all processes. Always balance the current level DFD's net inputs and outputs with those of the previous level.
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