# Build a decision requirements diagram

The requirements diagram says which decisions exist, what data they need, and what governs them. Drawing it first stops you writing one enormous table that should have been three.

The authority links are the part auditors ask about: which policy or regulation a rule comes from.

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## What this is for

* Any decision built from more than one sub-decision.
* Governance work, where the source of a rule matters.
* Planning before writing any table logic.

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## How it works

| **Action**               | **How**                                                       |
| ------------------------ | ------------------------------------------------------------- |
| Decision                 | A rectangle. Produces an output from its inputs.              |
| Input data               | Rounded ends. Data supplied from outside the model.           |
| Business knowledge model | Clipped corners. Reusable logic several decisions share.      |
| Knowledge source         | Wavy bottom. The authority: a policy, a regulation, a person. |
| Information requirement  | Solid arrow, into a decision.                                 |
| Authority requirement    | Dashed arrow, from a knowledge source.                        |

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## A few things that catch people out

* Solid and dashed arrows mean different things. Information flows; authority governs.
* A decision with five information requirements is usually two decisions.
* Name knowledge sources specifically. "Policy" helps nobody; "Credit policy 2026 v3" does.

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## Related

[Build a DMN decision tableInputs, outputs, rules, hit policy.](https://help.gocapable.com/diagrams/build-a-dmn-decision-table.html)

[DMN literal expressionsWhen a table is the wrong shape.](https://help.gocapable.com/diagrams/dmn-literal-expressions.html)

[DMN editorBack to the editor overview.](https://help.gocapable.com/diagrams/dmn-editor.html)

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_Draw the map before writing the rules._