Post-coordination (TermInfo Hot Topic)

At the January 2013 WGM in Phoenix the Vocab WG decided that the existing (but never started) Project 743 on "Guidance for the use of Terminology Post-Coordinated Expressions in HL7" should be closed and the topic most likely should be incorporated into TermInfo. This is the relevant excerpt from the Phoenix WGM minutes:

Project 743: Guidance for the use of terminology post-coordinated expressions in HL7

Can this be incorporated into the TermInfo Project? This is a topic that appears to be in the scope of TermInfo includes V2 and V3 and therefore should incorporate this project.

Action: Work with the TermInfo Project to determine the answer to this question (Rob H).

Project 743 Documentation

Project Scope

This project will create and document a set of policies and recommended procedures for the HL7 community relative to post-coordination in terminology as used in HL7 models and messages. It will examine the following:

1) What qualifies a terminology to be permitted to post-coordinate?

2) What existing guidance on post-coordination exists for eligible terminologies?

3) What should the HL7 guidance be on allowances and prohibitions for the use of post-coordination within a specific model. For example, should post-coordination supersede the information model by fully specifying semantics that are represented as concrete attributes?

4) What should be the style guidance on post-coordinated expressions (refer back to termInfo)

5) What, if any, might be potential data type changes that might be needed (particularly in version 2.x) to implement this guidance?

6) Within version 2.x, evaluation of the benefits of the use of post-coordination over the current sub_ID mechanism for communicating complex values.

7) Should there be guidance on which coded attributes should or should not allow post-coordination, and how should such guidance be formulated? Enforced?

8) For coded attributes that are currently constrained more tightly than CD, do these data type assignments need to be relaxed for post-coordination? What are the other impacts on existing models and balloted artefacts?

9) How does the post-coordination grammar look in the HL7 artifact, i.e. terse grammar, or fully expanded with descriptions (see 3)? What about terminologies that do not publish a grammar?

These questions, and probably others, will be examined and answered in the set of documentation to be produced by this project.

Project Need

Increasingly the HL7 community is asking for guidance for post-coordination, especially as SNOMED CT use increases throughout the world. There are many details that have not been adequately documented or addressed in the documents that have been developed to date.

Link to the original Project 743 PSS:

• File:2011SEP PSS Vocab BKnight PostCoordPolicy.doc