Data Flow Diagram Rules and Regulations

External Entity

Data Store

Data Flow

Process

1. A process must have at least one data flow entering and one data flow exiting the process symbol

2. All data flows must originate or terminate at a process.

3. A data store must be connected to a process with a data flow.

4. A data store should have at least one incoming and one outgoing data flow.

5. Data stores cannot be connected to another data store directly.

6. An external entity must be connected to a process by a data flow.

7. External entities only appear on a context diagram or Diagram 0.

8. Place data stores on the highest-level data flow diagram that has two or more processes using that data store.

9. A data store should only appear on one diagram.

10. Do no cross line.

11. No more than 9 process symbols should appear on one diagram.

12. Do not have depth of more than 7 levels.

13. Use a unique reference number for each process symbol. The reference number points to the DFD that contains the next level of detail for that process.

14. A context diagram has only one process, which is numbered 0.

15. A context diagram has no data stores and must fit on one page.

16. A Diagram 0 repeats the same external entities and data flows that appear in the context diagram.