Round tripping: How to handle unbound nested elements in shex?

[dbooth-boston]

In FHIR, we want them to not be there. How should shex allow this?

For example, FHIR allows setting of:
fhir:Patient.active [ fhir:value "true"^^xsd:boolean ] ;
But if no value is bound, then it comes through as:
fhir:Patient.active [ fhir:value <undefined> ] ;
when we want it to not produce either a fhir:value triple or a fhir:Patient.active triple. Even if we eliminate the immediate triple, we still do not want to emit a triple with an orphan bnode:
fhir:Patient.active [ ] ;

How should this be indicated to shex?

[dbooth-boston]

Maybe have a policy:

1. Eliminate any triple with an undefined S/P/O.
2. Eliminate any triple with an orphaned implicit bnode. This might require distinguishing between explicit and implicit bnodes.