Data flow diagrams: symbolising and explaining external entities, processes, data stores and flows

What this note covers

1. Gane–Sarson symbols and what they mean
2. The rules that make a DFD valid
3. Worked example: a library e-book loan service
4. Explaining a DFD: describe versus explain
5. Linking DFDs to algorithms, security and data exchange
6. Exam technique and common DFD errors

6 sections · 10 key terms & formulas · 6 common mistakes