ok, we have real convergence here. OpenEHR works exactly like HL7 - define a reference model with all the needed semantics, and then refine things away in constraint models (and use the refinements as a basis for composition). So the principle is the same.
We can generate [class models|schemas|wire formats] from constraint patterns. Doing so has benefits and costs. The same benefits and costs in either HL7 or OpenEHR. And one of the clear costs relates to persistence. I think we need to search for a better way, but that's not going to happen in the short term. But the OpenEHR & HL7 reference models are quite different. In most parts, the HL7 reference model is more abstract (Which is way Act gets 22 attributes). So harmonising between the reference models is going to require actual change rather than adroitly altering perspectives, as with data types and the constraint model things. This will be hard, and painful. And it must involve compromise, so this is when we find out who really values collaboration. And we don't want to take away the real benefits that OpenEHR has in the process (same for HL7) Grahame
