Expressions are produced as part of a fully validated approach including the appropriate knowledge and resources. As part of this approach occasionally expressions will fail validation, following which a review involving the check list (see process diagram above) below may be helpful. The commonest problem is a simple "syntax" error, or it may be that invalid (new or inactive) SNOMED terms are used in the expression which are not in the validation server version which currently lags behind by over a year.
The final step in the process should be a review and clinical sign off, considering that it is quite possible to construct and validate an expression which does not make sense. The step above Transform and Classify refers to the terminology server design 5.2.5 Validate and Transform Expression, which describes the system processes.
As the final step in the authoring process the expression should undergo final review NS sign off .