ProcessSample
Data flow diagram
Shows how data moves: from external entities, through processes that transform it, into and out of data stores. No timing, no decisions, just data.
Try this
- 01Switch between Gane–Sarson and Yourdon: the symbols change, the meaning does not.
- 02Click 3.0 Fulfil order and read what it receives and sends. Every process must turn some input into some output.
- 03Read the rules check: data never jumps straight from an external entity into a store. A process always sits in between.
Notation
- External entity (square)
- A person or system outside the boundary that sends or receives data.
- Process
- Transforms incoming data into outgoing data. Numbered (1.0, 2.0) so it can be exploded into a lower-level diagram.
- Data store (open box)
- Data at rest: a table, a file, a queue. Numbered D1, D2.
- Data flow (arrow)
- Data in motion, always labelled with what it carries.
- Gane–Sarson vs Yourdon
- Two symbol sets for the same ideas: rounded boxes versus circles for processes.
Use it when
- Scoping a system or a data pipeline
- Finding where personal or sensitive data travels (privacy reviews)
- Explaining a system to non-technical readers
Avoid it when
- Order, timing or decisions matter (use BPMN or a sequence diagram)
- Modelling the structure of the data itself (use an ERD)
More in Process
BPMN process diagram
Business Process Model and Notation: who does what, in which order, with decisions and parallel work, laid out in swimlanes.
UML sequence diagram
Who talks to whom, in what order, for one scenario. Time runs down the page; each arrow is one message between participants.
State machine diagram
The life of one object: the states it can be in, the events that move it between them, and the conditions that must hold. Anything not drawn is not allowed.