I've been exchanging a few e-mails with freinds in Australia familiar with openEHR. In a recent exchange they described some important ideas that I'd like to share:
In a comparison of two different standards used for the same purposes (their focus was openEHR and HL7 RIM, but this applies to any two standards):
The overlap, or intersection where both agree, denotes a least upper bound on that which is required to be standardized for representing information.
The superset shows where different approaches to the same issue are possible. I'd be a bit more specific and say that the set difference (the superset minus the intersection) show where variety is possible.
Applying these ideas to openEHR and CDA will take some time for analysis, however, applying this thinking to CDA and CCR:
The intersection between the two is CCD, and since CCD is an implementation of CCR, wholely subsumes CCR. The superset is CDA.