Chapter 4 – DFD Level Diagram Violation Rule

1. Data source ——- Data source: Wrong
2. Data store ——- Data store: Wrong

3. Data source ——- Data store: Wrong

4. A processing step may have input flows but no output flows.
This situation is sometimes called a black hole.
5. A processing step may have output flows but now input flows.
This situation is sometimes called a miracle.
6. A processing step may have outputs that are greater than the sum of its inputs – e.g., its inputs could not produce the output shown.
This situation is sometimes referred to as a grey hole.
The > Rule.

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