# Concepts

## Overview

Concepts can be added to an extension, either to address content gaps or to expand the scope of SNOMED CT to include concepts that are used locally. Extension concepts are distributed in a [concept file](https://app.gitbook.com/s/irKbJsZG57nSWZA4GT0M/component-release-file-specification/4.2-file-format-specifications/4.2.1-concept-file-specification), which follows the standard [RF2 release file format](https://app.gitbook.com/o/h8Z6qGxuQrzM9vbx5bPT/s/irKbJsZG57nSWZA4GT0M/). For more details on the principles and processes for authoring concepts in an extension, please refer to [Authoring Concepts](https://docs.snomed.org/snomed-ct-practical-guides/snomed-ct-extension-guide/5-key-steps/5.4-authoring/5.4.2-authoring-concepts).

## Attributes

In addition to the four [common attributes](https://docs.snomed.org/snomed-ct-practical-guides/snomed-ct-extension-guide/4-logical-design/4.3-extensions/4.3.1-components/4.3.1.1-common-attributes), extension concepts also have a definitionStatusId.

### definitionStatusId

The definitionStatusId attribute specifies whether the concept is [primitive](https://confluence.ihtsdotools.org/display/DOCGLOSS/primitive+concept) or fully defined. If defining relationships are added, which sufficiently define the concept, then the definitionStatusId should be set to [| Defined|](http://snomed.info/id/900000000000073002) . Otherwise, the extension concept is [| Primative|](http://snomed.info/id/900000000000074008) .

## Example

In the image below, a row from the concept table of the 20170901 US edition is shown, which represents the concept [5281000124103 | Persistent asthma|](http://snomed.info/id/5281000124103) .

Note that the attribute values in this row have been set according to the rules previously described.

<figure><img src="https://3979592733-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F3RKZIWpWFT0ocCgNT16E%2Fuploads%2Fgit-blob-6f053e6d8dc3cf65aba71b32b4e440995761ceb7%2F57815094.png?alt=media" alt=""><figcaption><p>A row from the concept table in the 20170901 US Edition</p></figcaption></figure>

Please note the following:

* The concept id uses a namespace identifier allocated to the National Library of Medicine (NLM). This indicates that this concept was originally created by the NLM.
* The concept id uses a partition identifier of “10”. This indicates that the concept was created in an extension.
* The moduleId indicates that this concept is included in the [| US National Library of Medicine maintained module|](http://snomed.info/id/731000124108) , which is a module in the US Edition.
* The definitionStatusId states that this concept is [| Primitive|](http://snomed.info/id/900000000000074008) .

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