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Thursday, June 11, 2015

Should HL7 support Backwards Compatible only, or Backwards compatibility as an option in the CCDA 2.1 DSTU Update?

One of the outstanding questions that the C-CDA project has to address is whether the 2.1 DSTU will require backwards compatibility only, or whether there will be a mode supporting backwards compatibility, and a mode where C-CDA 2.0 constraints are simply adopted.  We haven't made a decision yet.

Some would argue that supporting backwards compatibility only will simplify the guide for people. I have argued that will require HL7 to create a new project further down the line, and will not enable C-CDA 2.1 to be used in projects which are presently dependent upon C-CDA 2.0, some of which, like QRDA, also have a regulatory component naming a version of the standard.

To move forward, I will be proposing the following wording be adopted in constraints that are added to support backwards compatibility:
To support backwards compatibility, XXX SHALL/SHOULD/MAY YYY
This highlights the constraints added to support backwards compatibility.  Then we add language to the top of the specification depending upon which choice we make:

  1. If we choose backwards compatibility only, we state:
    This specification adds constraints supporting backwards compatibility.  These constraints are identified by beginning with the phrase "To support backwards compatibility", and are otherwise equivalent to any other constraint.
  2. If we choose to support both, we state:
    This specification adds constraints supporting backwards compatibility.  These constraints are identified by beginning with the phrase "To support backwards compatibility."  These are conditional constraints. When a document instance declares that it is supporting backwards compatibility by [mechanism to be established], these constraints must also be followed.  
This will allow the project team to create the constraints now, and make the choice later about whether these constraints are conditional or not.

HL7 is looking for feedback on this.  If you are a member of the Structured Documents mailing list, you can provide your feedback there, or on next weeks Thursday call, or on tomorrows C-CDA 2.1 DSTU Update project call.  As always, any feedback you provide in comments here, I will also forward to the workgroup, supporting them as best as I am able even though I have my own preferences.

Personally, I could still be convinced for option 1 by an argument that resonates with my own concerns, but am still strongly leaning towards option 2.