FHIR Chat · Re Must Support for reference types

Stream: argonaut

Topic: Re Must Support for reference types

Eric Haas (Dec 14 2020 at 18:16):

I received this question re subject/patient element

If you look at target field for AllergyIntolerance.patient field, it declares Patient and Group as possible target types. But in structure definition, patient field can only have references to Patient resource, NOT Group:
http://hl7.org/fhir/us/core/SearchParameter-us-core-allergyintolerance-patient.json.html
http://hl7.org/fhir/us/core/StructureDefinition-us-core-allergyintolerance.html

The same applies to patient search parameters in other resources.
Can you help to understand why this is the case?

Eric Haas (Dec 14 2020 at 18:24):

An implementer can adopt a US Core structure with patient/subject != patient reference, BUT it is not conformant to the specification. The scope of US Core is accessing patient data and all the profiling and search capablilities and guidance is tailored to the Patient as subject.

Aziz Khalmukhamedov (Dec 14 2020 at 18:49):

Thanks Eric.
If the scope of US Core is Patient data, why 'Group' is declared as a possible target type in search parameter definition? If we look at https://www.hl7.org/fhir/allergyintolerance.html, it says patient field can only have Patient references the same as the US Core structure definition. Shouldn't 'Group' be removed from target types since having non patient reference will not be conformant with specifications?

Eric Haas (Dec 14 2020 at 20:13):

can you point out exactly where a US Core search requirement allow group?

Vassil Peytchev (Dec 14 2020 at 20:31):

I think the question is:
If the base specification only allows references to Patient in AllergyIntolerance.patient, why does the definition of the Patient search parameter has as targets both Patient and Group - look at the "target" field in the JSON?

Aziz Khalmukhamedov (Dec 14 2020 at 21:21):

It's in search parameter definition:
http://hl7.org/fhir/us/core/SearchParameter-us-core-allergyintolerance-patient.json.html

"type" : "reference",
"expression" : "AllergyIntolerance.patient",
"xpath" : "f:AllergyIntolerance/f:patient",
"xpathUsage" : "normal",
"target" : [
"Patient",
"Group"
],

Eric Haas (Dec 14 2020 at 21:43):

1) These SP are defined only for conformances as noted here: http://hl7.org/fhir/us/core/searchparameters.html#search-parameters
2) They are derived from the base specification definitions and that is indeed an issue with the base SearchParameter Definition "clinical-patient' - thank you for discovering it. I will make a tracker to the base specification if one does not already exist. ( need to check ) The target for patient should be Patient.