# Validating

Compositional Grammar expressions can be automatically validated to ensure that they conform to a variety of rules, including:

* Expressions must conform to the syntax defined before. This validation can be performed using an expression parser;
* Expressions must conform to the concept model. This validation can be performed by comparing the parsed expression against the rules defined in the SNOMED CT concept model;
* All concept references included in the expression must be valid. In most cases this means that the concept references must refer to active concepts in the given version and edition of SNOMED CT.

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