# 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 v2.3.

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<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></tbody></table>

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