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Friday, May 16, 2014

Regional Adaptations of CDA Templates

One of the outcomes of last years work in IHE on attempting to utilize the CCDA templates was an approach to template constraint for regional and national projects that can simplify documentation.

Rather than creating templates constraining a first set of adopted templates, we looked at using the realmCode element within the document to "Nationalize" or "Regionalize" or "Localize" templates. RealmCode in the HL7 RIM is defined thus:
When valued in an instance, this attribute signals the imposition of realm-specific constraints. The value of this attribute identifies the realm in question.
So this becomes a completely appropriate approach to localization for regional or national projects.

Why does this simplify things?  Because it addresses the idea that regional constraints for the use of CDA are approached from a different perspective, usually dealing with vocabulary / value-set bindings for the region, or various namespaces used for various kinds of identifiers.  In PCC we sort of cobbled together the notion of Identity domains based on the HL7 notion of Concept Domains, which allows RealmCode to be used to support binding of specific identifier namespaces to identity domains.

How would you validate these constraints?  Generally you'd do something like this using the old way of creating a new template for the locale:
In this XML Context:  //*[cda:templateId/@root='locale-specific-template-oid']
Verify this rule is true: cda:code/@code = 'X' and cda:code/@codeSystem='Y'

But using realmCode, you'd do something like this:

In this XML Context:  //*[cda:templateId/@root='standard-template-oid-adopted-by-realm' and /*/cda:realmCode/@code='locale-specific-realm-code']
Verify this rule is true: cda:code/@code = 'X' and cda:code/@codeSystem='Y'

From a locale-specific testing basis, since realmCode/@code is expected to be your locale, you could even omit that second operation, and simply invoke a set of tests when your realm is asserted in the document.

HL7 and ISO will soon be embarking upon the development of a set of internationalized templates for the CCD (and hopefully all of CCDA over a longer time period).  I'm hoping we can redefine CCDA in terms of US Realm specific requirements on that internationalized effort.  It will make all our lives that much easier.


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