> 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/s/substrate.md).

# substrate

## substrate

The SNOMED CT content by which an expression constraint is evaluated or a query is executed.

#### Notes

* Two distinct types of substrate are directly relevant to use of SNOMED CT:
  * The *substrate* for an expression constraint that generates the membership of a subset or reference set.
  * The *substrate* for a clinical analytics query, consisting of a collection of records either coded in or mapped to SNOMED CT.

#### Examples

* Substrates for subset generation include:
  * A particular version of a specified SNOMED CT edition
  * Members of a preexisting reference set.
* Substrates for analytics include:
  * SNOMED CT encoded electronic health records from a particular institution or department.
  * A disease registry database containing or mapped to SNOMED CT.

##

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