Documenting Value Sets for External Code Systems

Template:MnM Open Closed Topic During the March 16, 2010 Harmonization Meeting, the participants discussed the challenge of how to document value sets that were defined against "external" code systems (ones that are not maintained by HL7) and are needed for HL7 specifications.

The issue was raised by Ted Klein. The participants included: Ted, Lloyd McKenzie, Austin Kreisler, Gregg Seppala, Wendy Huang, Mead Walker, Sandy Stuart, Rob Hausam, Woody Beeler and Russ Hamm.

After vigorous discussion, the group agreed unanimously to post the following points of agreement which indicate a likely path for dealing with this question. The points are:

1. We prefer to document value sets defined against external code systems, where required to support universal HL7 designs and HL7-published universal implementation guides, rather than to leave them undocumented.

2. We prefer not to add a sub-set of external code system codes into the Access DB in order to allow the enumeration of value sets in the DB.

3. The only vehicle [for documentation] available would appear to be MIF representation, because the current DB cannot support enumerations of codes not in the DB and has a very few forms of "intentional" definition.

4. Use of MIF2 is felt to be little (or no) more onerous than creating VML files.

5. Using MIF files will provide:
   1. Common source of truth (a single, merged MIF file).

   2. (Perhaps) Limited review via tools like RoseTree (although only codes)

   3. Publishing via the existing Vocab HTML representation (although with content limited to intentional expressions and enumerations of concept IDs.)

6. Using MIF files will require:
   1. A process for versioning the "supplementary" MIF file.

   2. A process for instantiating the value set definitions into MIF, in the first place.

   3. A standard procedure for combining the DB-generated MIF with the supplementary MIF and "validating" these files (XML-wise).

   4. Verification of the "renderings" by RoseTree and the HTML transforms.
7. Proposals for Such Value Sets must include
   1. That the external code system have its OID documented in the HL7 OID Registry

   2. That the proposal include the "registration" of the code system within the HL7 Vocabulary Maintenance process (in the Access data base)
   3. That the proposal include the correct OID for the external code system
   4. That the proposed value sets be registered in the HL7 OID registry as "HL7 maintained" value sets.
   5. That the proposal include the value set OID as registered in the OID registry.