A number of approaches exist to enable querying over SNOMED CT compositional grammar expressions. The recommended approach, however, is to first parse, translate (into OWL 2 EL) and classify the expressions together with the precoordinated content of SNOMED CT. A query language (such as the SNOMED CT Expression Constraint language, SNOMED CT Query language, SPARQL or DL Query) can then be used to construct queries, which are similarly parsed, translated and executed using an appropriate query engine. For more information about the SNOMED CT expression constraint and query languages, please refer to [Error! Reference source not found.] and  respectivelythe Expression Constraint Specification and Guide and SNOMED CT Glossary respectively.
An alternative approach to querying by testing two expressions for equivalence and subsumption is to transform each expression into its normal form and perform a comparison between the two normal form expressions. For more information on testing equivalence and subsumption between expressions using this approach please refer to section 126.96.36.1992.5 of the SNOMED CT Technical Implementation Guide .
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