Heath Frankel wrote:
Dear Sam, etal,
I wonder if the specialised schema approach for archetypes is one that
openEHR should encourage. Not so much discourage the investigation but at
least indicate to those who are going down this route that previous work by
Ocean and DSTC has indicated that the approach is not workable in a dual
layer model approach. Perhaps the more useful task is to find a suitable
schema for ADL if this has not already been done for which archetype
definitions can be validated against, not instances.
an XML-schema for the Archetype Object Model will be available very soon, initially probably as a hand-built one, but with the X-openEHR specification converter, we will be able to generate schemas for the entire RM and AM from that.
Perhaps it should be encouraged to use some existing schema's such as OWL
but again this is representing the archetype definition not the archetype
instance.
OWL I think is still research in this area; it has very weak leaf level semantics (which are known by the OWL community); we are working with the experts including prof Alan Rector and Rahil Qamar at University of Manchester to understand better how to "do archetypes in OWL".
Perhaps, the DSTC approach to represent archetypes using XML with a XML
schema for the Archetype Model should be endorsed by openEHR if this is the
preferred approach so people don't waste their time and develop a
proliferation of approaches which are likely to be incompatible or at least
require translation.
this is indeed the intended view, although I have recently come to the realisation that archetypes (or more properly openEHR templates - particular aggregations of archetypes) can be used to generate XML-schemas as well as XML-instance; the former would be usable as message definitions, for those who love messages. This would actually provide, for the first time, a single source development framework for software, schemas, screen definitions, and messages - all obeying coherent, consistent reference model, archetypes, templates and teminologies.
What would be better use of peoples time would be the investigation of an
archetype instance validating parser that uses the XML document representing
the archetype definition similar to an XML validating parser uses xml schema
(which is also an XML document).
this is indeed one thing that is needed; personaly, I would do it by reading in the archetype and the data from XML form into a DOM-tree and jst using the kernel to do the work.
The reason we need to have an XML document represent the archetype is
because of the dual layer model approach where the XML schema is used at the
reference model level and an xml instance can't have two associated schemas
for validation for each level. However, from my understanding (which is
limited), this is not an issue in some of these other schema systems like
Schematron and RelaxNG, so it might be useful for people to investigate
these if they really want to represent archetypes as XML schema's but
knowing that traditional parsers and XML tools will not support this due to
the dual layer model approach.
I also have suspicions that these other schema types might in fact be better for our purposes than XML-schema, and I hope others might be able to provide expert input on this.
- thomas