Data flow diagram
Definition
A data flow diagram (DFD) is a structured analysis tool that shows how data moves through a system, using four symbols: external entities, processes, data stores, and data flows.
Ed Yourdon and Larry Constantine formalized DFDs in the 1970s as part of structured analysis — a method for designing software systems before object-oriented approaches dominated. Despite being older than UML, DFDs remain widely used in security (threat modeling), data governance, and systems analysis because they focus on data rather than code or services.
The four DFD symbols:
- External entities (rectangles): people or systems outside the scope of the diagram that send or receive data
- Processes (circles or rounded rectangles): transformations that change or move data
- Data stores (parallel lines): where data rests between processes — databases, files, queues
- Data flows (arrows): data in motion, labeled with the data's name
DFDs come in levels. A Level 0 (context) diagram shows the whole system as a single process and its relationships to external entities. A Level 1 diagram explodes that process into its main sub-processes. A Level 2 diagram further decomposes each Level 1 process.
In security and compliance work, DFDs are required artifacts for threat modeling (STRIDE, DREAD) — you must draw a DFD before you can identify trust boundaries. Teams draw them on whiteboards during security reviews and compliance audits. BoardSnap AI reads the entities, processes, stores, and flow arrows to produce a structured summary.
Examples
- Level 0: User sends login credentials to 'Authentication system,' which accesses User database and returns session token
- Level 1 e-commerce: Order process decomposes into Validate cart, Charge payment, Confirm inventory, and Dispatch shipping
- GDPR compliance DFD: showing where personal data enters the system, what processes touch it, and where it's stored
- ETL pipeline DFD: Source databases → Extract process → Staging store → Transform process → Data warehouse → Reporting process
Snap a data flow diagram. Ship its actions.
BoardSnap turns any whiteboard — including this one — into a summary and action plan.