# Exchanging

There are a number of alternative techniques that may be used when exchanging SNOMED CT expressions in messages. These include:

* Placing the full SNOMED CT compositional grammar expression in the relevant *code* field of the message.
  * For example, the HL7 version 3 CD data type (Release 2) allows the 'code' property to include SNOMED CT expressions (see [HL7 TermInfo guide](http://wiki.hl7.org/index.php?title=File:V3_IG_SNOMED_R1_D5_2014JAN.docx)).
* Using an alternative structure for representation of the logical structure of an expression.
  * For example an OWL serialization.
* Placing a unique expression identifier in the relevant *code* field of the message
  * This approach requires the use of a shared expression repository enabling the recipient system to look up and resolve this identified to the relevant expression.
* Decomposing the expression into separate codes that can be placed in different fields within the message structure.
  * This approach assumes alignment between the message structure and the relevant parts of the SNOMED CT concept model.

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