Implementation FAQ:Migration from version 2

This page contains questions related to the migration of HL7 version 2 to version 3, mostly from a non-technical perspective.

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Questions

Selling point for V3

Question: What is the real value of the reference model in V3 – what is the life of the system –this can be a long time for strategic programs. These need to be future-proofed.

• Two documents from the Marketing Committee's document page that discuss the rationale for using HL7 version 3:
  • Draft HL7 v3 Value Proposition Document
  • Canada Infoway v3 Infosheet

Question: I have a running system using V2, how do I justify moving to V3, especially as V2 just keeps getting better.

• The justification of v3 lies in those areas that v2 doesn't cover (e.g. inter-organizational communications, CDA, clinical genomics).

v3 equivalent of v2 null

Question: In v2, "" (null) is used to inform the receiver that "any value it has for the field should be erased from its database". What's the equivalent in v3?

• Closest thing would be an UpdateMode of "delete"
• If you're in snapshot mode (i.e. not operating using updateMode), then it's up to the receiver whether they choose to get rid of information you don't supply.
• Even with updateMode, if it's a Notification, you're simply stating what you've done, not what the receiver must do. Only with a Request would the receiver be obligated to actually remove the value (and then only if they agree to act on the overall request).

Recommendations

Don't assume v2 - v3 mapping can be done at the integration layer

If your application already supports HL7 v2: HL7 v2-v3 migration by means of a mapping is problematic. The main problem is not the mapping itself (although HL7 v3 is much more detailed than HL7 v2), but the behaviour of the application. This is mainly a business flow issue. The dynamic behaviour and trigger events in V2 and V3 are sufficiently different, that your application behaviour will need to map on to them differently.

• If your application has to support both HL7 v3 as well as HL7 v2: create a new communication module for the HL7 v3 messages/documents, and use it in parallel to the HL7 v2 communication module.
• If one has an application which has a v2 interface (and where the creation of a new fullblown v3 interface is not an option - for whatever reason), it may be relatively easy to enrich an existing message (using Z-segments if need be) with content needed to populate a v3 message. Translation can then be done by a communication server. Such an approach would ease the mapping problem.