> For the complete documentation index, see [llms.txt](https://docs.snomed.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.snomed.org/snomed-international-documents/snomed-ct-glossary/n/nnf.md).

# nnf

## NNF

**This is an abbreviation for necessary normal form.**

## necessary normal form

An inferred view of a concept definition that includes only defining relationships that are necessarily true.

#### Notes

* The necessary normal form is designed to represent an inferred view derived from the enhanced concept definitions in a form that can be distributed in the relationship file. Although the enhanced features cannot be fully represented within the structure of the relationship file, the necessary normal form provides a view of the results of classifying data that is accessible to those without access to description logic tools.

#### Change Notices

* Changes introduced in the July 2019 release of the International Edition, enhanced the ability of SNOMED CT to support more advanced description logic. These changes allow the stated view of concept definitions to use axioms represent using the OWL Functional Syntax.

## Alternatives

* **NNF**

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