DFD notation and why it matters
A data flow diagram uses four element types from Yourdon/DeMarco notation: rectangles for external entities (people or systems outside your boundary), circles for processes (transformations), parallel lines for data stores (databases or files), and arrows for data flows with named payloads. Using the correct notation makes DFDs readable by any analyst, developer, or auditor without a legend.
flow-chart.io generates properly notated DFDs, not generic box-and-arrow diagrams. Each element type has its correct shape, and each flow arrow carries a data label — the name of what's actually moving between components.
What flow-chart.io generates for data flow diagrams
- Level 0 (context diagram) — your entire system as a single process with all external entities and boundary flows
- Level 1 — the system decomposed into its major processes, data stores, and the flows between them
- Level 2 — a single Level 1 process expanded into its sub-processes and internal data stores
- Correct Yourdon/DeMarco shapes — rectangles, circles, parallel-line stores, labeled arrows
- Named data flows — every arrow labeled with the data payload it carries
- GDPR data mapping support — mark personal data flows for privacy impact assessments
How to generate a data flow diagram
- Sign up free — 5 diagrams, no credit card required.
- Select the Data Flow Diagram domain in the diagram type picker.
- Describe your system — e.g. "Online store: Customer places Order → Order Processing validates against Product Catalog and Customer DB → sends Confirmation to Customer, updates Inventory, forwards to Fulfillment system."
- Choose a level — generate the context diagram first, then drill into Level 1 and Level 2 as needed.
Frequently asked questions
- What notation does flow-chart.io use for DFDs?
- Yourdon/DeMarco notation: rectangles for external entities, circles for processes, open-ended parallel lines for data stores, and directed arrows labeled with data names. This is the most widely used DFD notation in software engineering and systems analysis.
- Can I use DFDs for GDPR data mapping?
- Yes. DFDs are a standard tool for mapping personal data flows. You can annotate flows as containing personal data and export the diagram for inclusion in your Records of Processing Activities (RoPA) documentation.
- How do Levels 0, 1, and 2 relate?
- Level 0 shows your system as a single process interacting with external entities — a high-level context view. Level 1 decomposes that process into its major sub-processes. Level 2 decomposes one Level 1 process further. Each level is a separate diagram generated from the same system description.
- Is this different from a flowchart?
- Yes. A flowchart shows the sequence of steps in a process. A DFD shows what data exists, where it comes from, where it goes, and what transforms it. They answer different questions and use different notation.