# Expression Constraint Language - Specification and Guide

The *Expression Constraint Language* is a formal syntax for representing SNOMED CT expression constraints. Expression constraints are computable rules used to define a bounded set of clinical meanings represented by either precoordinated or postcoordinated expressions. Expression constraints can be used to restrict the valid values for a data element in an EHR, as the intensional definition of a concept-based reference set, as a machine processable query that identifies a set of matching expressions, or as a constraint that restricts the range of an attribute defined in the SNOMED CT concept model.

This document defines and describes the current version of the Expression Constraint Language - ECL v2.2.

***

<table data-view="cards"><thead><tr><th data-type="content-ref"></th></tr></thead><tbody><tr><td><a href="1-introduction">1-introduction</a></td></tr><tr><td><a href="2-use-cases">2-use-cases</a></td></tr><tr><td><a href="../examples">examples</a></td></tr><tr><td><a href="../implementation-considerations">implementation-considerations</a></td></tr></tbody></table>

***

{% hint style="info" %}
© Copyright 2025 International Health Terminology Standards Development Organisation, all rights reserved.

This document is a publication of International Health Terminology Standards Development Organisation, trading as SNOMED International. SNOMED International owns and maintains SNOMED CT®.

Any modification of this document (including without limitation the removal or modification of this notice) is prohibited without the express written permission of SNOMED International. This document may be subject to updates. Always use the latest version of this document published by SNOMED International. This can be viewed online and downloaded by following the links on the front page or cover of this document.

SNOMED®, SNOMED CT® and IHTSDO® are registered trademarks of International Health Terminology Standards Development Organisation. SNOMED CT® licensing information is available at <http://snomed.org/licensing>. For more information about SNOMED International and SNOMED International Membership, please refer to [http://www.snomed.org](http://www.ihtsdo.org/) or contact us at [info@snomed.org](mailto:info@ihtsdo.org).
{% endhint %}

<a href="https://docs.google.com/forms/d/e/1FAIpQLScTmbZIf0UEQwYDkY27EEWBkaiYkHSbR0_9DmFrMLXoQLyL7Q/viewform?usp=pp_url&#x26;entry.1767247133=ECL+Specification&#x26;entry.670899847=Expression%20Constraint%20Language%20-%20Specification%20and%20Guide" class="button primary">Provide Feedback</a>
