[Validator] Support profiles on backbone elements

[ewoutkramer]

What if.....

1. We create a logical model representing a Document.section Section
2. We create section profiles with this logical model as the base
3. Invent an extension "documentSectionProfile" that goes on the typeref for Document.section and which is a valueUrl with the canonical for the section profile
4. Let Grahame and me hack our validators to trigger validation via that logical model in STU3.

[wmrutten]

2. We create section profiles with this logical model as the base

As far as I'm aware, FHIR does not allow a profile to be based on a logical model?

[ewoutkramer]

Sure it does, why not? Same logic applies, it's just a set of constraints

[wmrutten]

Theoretically, yes. But FHIR has not formally defined this yet. Not supported in Forge.
Anyway we could decide to allow this, but it seems like a hack. IMHO proper approach is to elevate all backbone elements to proper data types. Then we wouldn't need to introduce new irregularities.

[ewoutkramer]

This was about fixing stuff in STU3 - with backwards compatibility, so defining proper data types is no solution...

[ewoutkramer]

There's now even an extension for it, so you can for example create profiles just for sections of a Document resource. But until someone asks, we'll wait to do this.