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Background

The AQL MATCHES statement may perform a request to a terminology server for performing some operation over a value set or code system (here used as a synonym of terminology). Several operations may be possible, being the most common ones: the expansion of a ValueSet (or Reference Set), checking that a concept belongs to a value set or code system, testing if one concept subsumes another one, or the translation of concepts across different terminologies.

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A less cumbersome approach has been agreed by using  a keyword (TERMINOLOGY) in the AQL syntax. The TERMINOLOGY keyword indicates that the three sections inside its parenthesis correspond to the operation, the driver or adapter for the external terminology server (e.g. HL7 FHIR TS, Ocean CTS, DTS2), and the driver identifiers. These identifiers should provide the necessary information for invoking external terminology servers to perform an operation. In addition, the AQL TERMINOLOGY operand should also provide the necessary information for allowing the processing system to parse back the response from the terminology server.

The MATCHES syntax should allow to directly use the TERMINOLOGY statement for indicating that the set will be resolved by the internal representation. This is already allowed by some implementers.

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