Create a post co-ordinated expression library

A post co-ordinated expression contains two or more concept identifiers to represent an idea. It is a SNOMED-CT notion that is relevant to FHIR resources that use SNOMED-CT.

A post co-ordinated expression is an expression that contains two or more concept identifiers  to represent an idea.

By creating a Post Co-ordination Expression (PCE) Library, you are making prepared PCEs available for inclusion in a ValueSet alongside individual SNOMED-CT Concepts. This examples demonstrates how to create a PCE library, and then including a PCE in a ValueSet.

1. Create a new Code System.  Here we have called it PCE Library supplement.  Make sure you add in a Code System URI so the Code System can be successfully uploaded to the Terminology Server.  Then change the content to Supplement (R4). The code system to supplement field will then be revealed.

In this example we want to create a PCE that can be used with any SNOMED-CT based FHIR ValueSet.  So we create a FHIR CodeSystem supplement for the SNOMED-CT CodeSystem.  You will need to chose the appropriate edition of SNOMED CT to supplement. 

2. Click on Find existing FHIR Resources, then change the Type of the search to CodeSystem.  Change the Value to SNOMED (to search for all SNOMED CodeSystems) and click on the + button to get a local copy of the latest available UK edition of the SNOMED-CT CodeSystem.

3. We will need to copy the Code System URI and the version field values into the Code System to Supplement field of our newly created supplement. The field accepts canonicals, which means it accepts the URI and the version as one string separated by a "|" character.

http://snomed.info/sct|http://snomed.info/sct/ 999000031000000106/version/20200204 

The supplement now looks like this:

You now need to add the PCEs to the supplement.  Add your Add your PCEs to the code column of the table (You can resize the column widths to give yourself more room to see the values of the code and display columns) . FHIR always considers SNOMED CT codes to be expressions, where a single code is the simplest form of an expression. You can optionally include a value for the display column.

4. Add your PCEs to the code column of the table - FHIR always considers SNOMED CT codes to be expressions, where a single code is the simplest form of an expression. You can optionally include a value for the display column.

5. Upload your supplement to the Terminology Server to make it available for use. Click on the Upload to FHIR Server tab, then click on Validate Code System to validate before uploading, then click on Upload Code system. This operation will take a few minutes while the supplement is classified and indexed for subsequent high performance querying.

When your code system supplement has been successfully uploaded you will get a confirmation message.

You have now created a PCE Library.