Quiz Entry - updated: 2026.07.14
What are the four main elements in Data Flow Diagram (DFD) notation?
Process (circle), Data Store (two parallel lines), Source/Sink (rectangle), and Data Flow (arrow) — four symbols that capture how data moves, without showing control flow or timing.
* A simple worked DFD showing processes, a data store, external entities, and labelled data flows. — AutumnSnow, GFDL / CC BY-SA, via Wikimedia Commons. *
| Element | Symbol | Examples |
|---|---|---|
| Process | Circle | Services, Components, DLLs, EXEs, Runtimes |
| Data Store | Open rectangle (two parallel lines) | File systems, Database, Registry, Memory, Stack, Queue |
| Source/Sink | Rectangle | People (Users), Systems |
| Data Flow | Arrow | Network traffic, Function calls, Procedure Calls (RPC) |
DFDs show how data moves through a system without specifying control flow or timing.
DFD Levels:
- Level 0 (Context Diagram): Single process representing entire system, showing external entities
- Level 1: Breaks down the main process into sub-processes
- Level 2+: Further decomposition as needed
Key rules:
- Data cannot flow directly between two data stores (needs a process)
- Data cannot flow directly between two external entities (outside system scope)
- Every process must have at least one input and one output
Go deeper:
Data-flow diagram (Wikipedia) — the four notation elements and the context-diagram / DFD-level hierarchy.