> 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/snomed-ct-expression-constraint.md).

# snomed ct expression constraint

## SNOMED CT expression constraint

A computable rule that is used to define a set of clinical meanings.

#### Notes

* *SNOMED CT expression constraints* are defined using the expression constraint language (ECL).
* *Expression constraints* can be used for a variety of purposes including:
  * Specifying value set bindings that constrain the values that can be entered in a particular data entry context.
  * Representing an intensional subset definition, which may be used to determine the membership of a reference set
  * Querying electronic health records for record entries that contain specified sets of concepts and/or expressions
  * Defining the SNOMED CT concept model by specifying the sets of concepts in a [| concept model domains|](http://snomed.org/fictid#) and the range of values applicable to each attribute.

##

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