# Data flow diagram

A data flow diagram answers a different question from a flowchart: not what happens in what order, but what data moves where. It has four elements only, which is why it stays readable when a flowchart of the same system would not.

Start at context level, one process and its external entities, then expand to level 1 only if you need to.

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## When to reach for one

* Privacy and data protection work, where the question is where personal data goes.
* Integration design, before anybody has written a connector.
* Explaining a system to someone who does not care about the code.

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## How to draw it in Capable

| **Route** | **Use when**                                                |
| --------- | ----------------------------------------------------------- |
| Graphviz  | Layout is automatic, which suits diagrams that grow.        |
| draw.io   | You want the classic DFD shapes and full control of layout. |

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## A worked example

A level 1 data flow diagram for an order system:

![Data flow diagram](https://help.gocapable.com/images/att1418493955.svg)

The source, which you can paste into a new diagram and edit:

```
digraph dfd {
  rankdir=LR;
  node [fontname="Helvetica"];
  customer [shape=box, label="Customer"];
  warehouse [shape=box, label="Warehouse"];
  order [shape=ellipse, label="1.0\nTake order"];
  fulfil [shape=ellipse, label="2.0\nFulfil order"];
  orders [shape=box, style=dashed, label="D1 Orders"];
  customer -> order [label="order details"];
  order -> orders [label="new order"];
  orders -> fulfil [label="pending orders"];
  fulfil -> warehouse [label="pick list"];
  fulfil -> customer [label="confirmation"];
}
```

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## A few things that catch people out

* Every process needs at least one input and one output. A process with only inputs is a data store you mislabelled.
* Do not draw control flow. Arrows carry data, not sequence.
* Number processes (1.0, 1.1) so level 1 and level 2 diagrams can refer to each other.

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## Related

[Decision treeBranching questions with one answer at the end.](https://help.gocapable.com/diagrams/decision-tree.html)

[Decision tableDMN rules with real hit policies.](https://help.gocapable.com/diagrams/decision-table.html)

[ExamplesWorking diagrams you can copy.](https://help.gocapable.com/diagrams/examples.html)

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_Draw the unhappy path too._