# canonical form

## canonical form

A serialized representation of a SNOMED CT expression produced by applying a set of rules that ensure a single unique representation for any expression.

#### Notes

* Expressions that contain exactly the same concept identifiers and refinements, may differ from one another in the following ways:
  * Inclusion of whitespace between elements
  * Inclusion of specific terms associated with identified concepts.
  * The order in which focus concepts, refinements, attributes, and attribute groups appear.
* The *canonical form* is generated by removing whitespace and terms from an expression and arranging the focus concepts, refinements, attributes, and attribute groups in a standard order.
* If *canonical form* rules are applied to a normal form expression, the result is a single unique rendering of the meaning represented by that expression.

## Alternatives

* **Canonical representation**

## Related Links

* Wikipedia
  * [Canonical form](https://en.wikipedia.org/wiki/Canonical_form)

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