# DMN requirement elements

The decision requirement diagram sits above the tables and shows structure: which decisions depend on which other decisions, what input data they need, and which knowledge sources govern them.

It is the map. The tables are the detail.

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## When it matters

* Decisions built from several sub-decisions.
* Governance work, where the authority behind a rule matters.

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## The symbols

| **Symbol**               | **Means**                                                             |
| ------------------------ | --------------------------------------------------------------------- |
| Decision                 | Rectangle. Produces an output from inputs.                            |
| Input data               | Rounded rectangle with flat ends. Data supplied from outside.         |
| Business knowledge model | Rectangle with clipped corners. Reusable logic.                       |
| Knowledge source         | Wavy-bottomed shape. The authority: a policy, a regulation, a person. |
| Information requirement  | Solid arrow. Data flowing into a decision.                            |
| Authority requirement    | Dashed arrow. A knowledge source governing a decision.                |

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## A few things that catch people out

* Knowledge sources are how you record that a rule comes from a specific regulation. Auditors ask.
* Information requirements are solid; authority requirements are dashed. They are not interchangeable.
* Draw the requirement diagram first. It shows how many tables you actually need.

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## Related

[DMN hit policiesWhat happens when two rules match.](https://help.gocapable.com/diagrams/dmn-hit-policies.html)

[FEEL expressionsThe little language inside the cells.](https://help.gocapable.com/diagrams/feel-expressions.html)

[DMN notation referenceBack to the full DMN reference.](https://help.gocapable.com/diagrams/dmn-notation-reference.html)

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_Pick the hit policy on purpose._