Purpose

The  is designed to enable associations between codes in another code system  and , where the following constraints apply:

1. Some of the  cannot be mapped to an individual SNOMED CT .
2. Licensing conditions (or other considerations) prevent addition of new SNOMED CT concepts to represent the same meaning as the .
3. The  can be logically defined using the  to represent the same meaning  or a similar though less specific meaning .
4. Other requirements similar for those applicable to mapping may also apply including:
   1. An indication of the degree of correlation between the   and the SNOMED CT expression.
   2. An indication of whether the  was created before any single concept representation of that meaning in SNOMED CT or whether the single concept representation in SNOMED CT predated the creation of the association.

Data Structure

The general approach to the above requirements is to associate each of the  with a representation of the same logic based definition as would have been applied to a SNOMED CT concept with that meaning. However, since the   are not identified by an  , the logical definition cannot be represented using  . There are two potential approaches to this, one would be to use a general purpose description logic language (e.g.  ) and the other is to use a  to represent each definition. The  is designed to support the expression-based approach.

Code to Expression Reference Set - Data structure

Code to Expression Reference Set in the Metadata Hierarchy

  900000000000454005 |Foundation metadata concept|
		900000000000455006 |Reference set|
				705109006 |Code to expression type reference set|

Refset Descriptor rows for a Code to Expression Reference Set

Sample Content from a Code to Expression Type Reference Set