> 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-ct-specifications/snomed-ct-release-file-specification/reference-set-release-file-specification/5.1.4-metadata-supporting-reference-sets.md).
# Metadata Supporting Reference Sets
Reference sets types are identified by concepts that are subtypes of the metadata concept [900000000000455006 |Reference set|](http://snomed.info/id/900000000000455006). Individual reference sets of a particular type are identified and named by concepts that are subtype descendants of the concept that identifies the reference set type.
***
**Reference Set Types in the Metadata Hierarchy (2018-01-31)**
[900000000000455006 **|****Reference set****|**](http://snomed.info/id/900000000000455006)\
[900000000000516008 **|Annotation type|**](http://snomed.info/id/900000000000516008)\
[900000000000521006 **|Association type|**](http://snomed.info/id/900000000000521006)\
[900000000000480006 **|Attribute value type|**](http://snomed.info/id/900000000000480006)\
[705109006 **|Code to expression type reference set|**](http://snomed.info/id/705109006)\
[447250001 **|Complex map type reference set|**](http://snomed.info/id/447250001)\
[609430003 **|Concept model reference set|**](http://snomed.info/id/609430003)\
[900000000000538005 **|Description format|**](http://snomed.info/id/900000000000538005)\
[733614007 **|Expansion history reference set|**](http://snomed.info/id/733614007)\
[609331003 **|Extended map type reference set|**](http://snomed.info/id/609331003)\
[733613001 **|Intensional definition reference set|**](http://snomed.info/id/733613001)\
[900000000000506000 **|Language type|**](http://snomed.info/id/900000000000506000)\
[705111002 **|Map correlation and origin type reference set|**](http://snomed.info/id/705111002)\
[900000000000534007 **|Module dependency|**](http://snomed.info/id/900000000000534007)\
[723564002 **|MRCM reference set|**](http://snomed.info/id/723564002)\
[733618005 **|Ordered association type reference set|**](http://snomed.info/id/733618005)\
[733619002 **|Ordered component type reference set|**](http://snomed.info/id/733619002)\
[447258008 **|Ordered type reference set|**](http://snomed.info/id/447258008)\
[900000000000512005 **|Query specification type|**](http://snomed.info/id/900000000000512005)\
[900000000000456007 **|Reference set descriptor|**](http://snomed.info/id/900000000000456007)\
[900000000000496009 **|Simple map|**](http://snomed.info/id/900000000000496009)\
[446609009 **|Simple type reference set|**](http://snomed.info/id/446609009)
{% hint style="info" %}
Other concepts within the metadata hierarchy are used to name additional attributes within particular types of reference sets and to provide values for those attributes.
{% endhint %}
***
**Reference Set Attributes in Metadata Hierarchy (2018-01-31) (some omitted)**
[900000000000457003 **|Reference set attribute|**](http://snomed.info/id/900000000000457003)\
[447257003 **|"Linked to" reference set attribute|**](http://snomed.info/id/447257003)\
[900000000000511003 **|Acceptability|**](http://snomed.info/id/900000000000511003)\
[900000000000518009 **|Annotated component|**](http://snomed.info/id/900000000000518009)\
[900000000000519001 **|Annotation|**](http://snomed.info/id/900000000000519001)\
[900000000000532006 **|Association source component|**](http://snomed.info/id/900000000000532006)\
[900000000000533001 **|Association target component|**](http://snomed.info/id/900000000000533001)\
[900000000000458008 **|Attribute description|**](http://snomed.info/id/900000000000458008)\
[900000000000479008 **|Attribute order|**](http://snomed.info/id/900000000000479008)\
[723576002 **|Attribute rule|**](http://snomed.info/id/723576002)\
[900000000000459000 **|Attribute type|**](http://snomed.info/id/900000000000459000)\
[900000000000491004 **|Attribute value|**](http://snomed.info/id/900000000000491004)\
[733616009 **|Authoring substrate|**](http://snomed.info/id/733616009)\
[723571007 **|Cardinality|**](http://snomed.info/id/723571007)\
[609431004 **|Concept model domain|**](http://snomed.info/id/609431004)\
[609432006 **|Concept model range|**](http://snomed.info/id/609432006)\
609642003 **|Concept model relationship type|**\
[723573005 **|Concept model rule strength|**](http://snomed.info/id/723573005)\
[723574004 **|Content type|**](http://snomed.info/id/723574004)\
[900000000000535008 **|Dependency target|**](http://snomed.info/id/900000000000535008)\
[900000000000539002 **|Description format|**](http://snomed.info/id/900000000000539002)\
[900000000000510002 **|Description in dialect|**](http://snomed.info/id/900000000000510002)\
[900000000000544009 **|Description length|**](http://snomed.info/id/900000000000544009)\
[723565001 **|Domain constraint|**](http://snomed.info/id/723565001)\
[733612006 **|Expansion substrate|**](http://snomed.info/id/733612006)\
[706999006 **|Expression|**](http://snomed.info/id/706999006)\
[900000000000514006 **|Generated reference set|**](http://snomed.info/id/900000000000514006)\
[723572000 **|Grouped|**](http://snomed.info/id/723572000)\
[723570008 **|Guide URL|**](http://snomed.info/id/723570008)\
[900000000000511003 **|Acceptability|**](http://snomed.info/id/900000000000511003)\
[609330002 **|Map category value|**](http://snomed.info/id/609330002)\
[900000000000501005 **|Map group|**](http://snomed.info/id/900000000000501005)\
[900000000000502003 **|Map priority|**](http://snomed.info/id/900000000000502003)\
[00000000000503008 **|Map rule|**](http://snomed.info/id/900000000000503008)\
[900000000000500006 **|Map source concept|**](http://snomed.info/id/900000000000500006)\
[900000000000505001 **|Map target|**](http://snomed.info/id/900000000000505001)\
[723577006 **|MRCM rule reference set|**](http://snomed.info/id/723577006)\
[705116007 **|Original code system source for linked content value|**](http://snomed.info/id/705116007)\
[723566000 **|Parent domain|**](http://snomed.info/id/723566000)\
[447255006 **|Priority order reference set attribute|**](http://snomed.info/id/447255006)\
[723567009 **|Proximal primitive constraint|**](http://snomed.info/id/723567009)\
[723568004 **|Proximal primitive refinement|**](http://snomed.info/id/723568004)\
[900000000000515007 **|Query|**](http://snomed.info/id/900000000000515007)\
[733615008 **|Query language|**](http://snomed.info/id/733615008)\
[733617000 **|Query string|**](http://snomed.info/id/733617000)\
[723575003 **|Range constraint|**](http://snomed.info/id/723575003)
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