Although there are many ways to draw DFD diagrams, they all start with a careful examination of existing systems or processes, careful thinking about what really happens, and careful choices about how to accurately represent what happens using the diagrams. Our diagrams in this appendix were fairly simple, although a lot of thought went into making decisions about them.
The basic steps of the process are these:
- Create or obtain an accurate and reliable narrative.
- From the narrative, create a complete table of entities and activities.
- Draw a context diagram with external entity boxes by distinguishing carefully between internal and external entities.
- Draw current physical flow diagrams by creating bubbles for internal entities, and showing flows to and from all entities and data stores.
- Draw current logical flow diagrams by grouping activities that occur together, and naming the logical sub-processes each describes. Remember to balance this diagram with the other diagrams by matching their external entities and their data flows.
Don’t let the rigor of the documentation get in the way of using the diagrams to understand the system. You have seen many guidelines, hints, and instructions to help you draw DFDs. Use your judgment in applying this information.