Stream: implementers
Topic: Element.id vs snapshots of subtypes of Element in FHIR 4.0.0
Gabriel Bezerra (Feb 22 2019 at 15:25):
Dear all,
In FHIR 4.0.0, Element.id is defined by the following ElementDefinition:
{
"id" : "Element.id",
"path" : "Element.id",
"representation" : ["xmlAttr"],
"short" : "Unique id for inter-element referencing",
"definition" : "Unique id for the element within a resource (for internal references). This may be any string value that does
"min" : 0,
"max" : "1",
"base" : {
"path" : "Element.id",
"min" : 0,
"max" : "1"
},
"type" : [{
"_code" : {
"extension" : [{
"url" : "http://hl7.org/fhir/StructureDefinition/structuredefinition-json-type",
"valueString" : "string"
},
{
"url" : "http://hl7.org/fhir/StructureDefinition/structuredefinition-xml-type",
"valueString" : "xsd:string"
},
{
"url" : "http://hl7.org/fhir/StructureDefinition/structuredefinition-rdf-type",
"valueString" : "xsd:string"
}]
}
}],
"isModifier" : false,
"isSummary" : false,
"mapping" : [{
"identity" : "rim",
"map" : "n/a"
}]
},
However, when looking into subtypes of Element, one can find the StructureDefinitions have the following shape:
{
"fullUrl" : "http://hl7.org/fhir/StructureDefinition/BackboneElement",
"resource" : {
"resourceType" : "StructureDefinition",
"id" : "BackboneElement",
// ...
"fhirVersion" : "4.0.0",
// ...
"kind" : "complex-type",
"abstract" : true,
"type" : "BackboneElement",
"baseDefinition" : "http://hl7.org/fhir/StructureDefinition/Element",
"derivation" : "specialization",
"snapshot" : {
"element" : [{
"id" : "BackboneElement",
// ...
},
{
"id" : "BackboneElement.id",
"path" : "BackboneElement.id",
"representation" : ["xmlAttr"],
"short" : "Unique id for inter-element referencing",
"definition" : "Unique id for the element within a resource (for internal references). This may be any string value that does
"min" : 0,
"max" : "1",
"base" : {
"path" : "Element.id",
"min" : 0,
"max" : "1"
},
"type" : [{
"code" : "string"
}],
"isModifier" : false,
"isSummary" : false,
"mapping" : [{
"identity" : "rim",
"map" : "n/a"
}]
},
{
"id" : "BackboneElement.extension",
// ...
},
{
"id" : "BackboneElement.modifierExtension",
// ...
}]
},
"differential" : {
"element" : [{
"id" : "BackboneElement",
// ...
},
{
"id" : "BackboneElement.modifierExtension",
// ...
}]
}
...that is:
- differential does not pose any changes to the id field; and
- snapshot shows an id field whose type is completely different from the definition of the base Element.id.
It also happens with other Elements, like http://hl7.org/fhir/StructureDefinition/string, http://hl7.org/fhir/StructureDefinition/boolean etc.
What is the correct version: the one described by differential, or the one described by snapshot?
Gabriel Bezerra (Feb 25 2019 at 09:08):
@Grahame Grieve @Lloyd McKenzie -- you usually answer my questions in this regard, maybe you would be interested in this one ^
Michel Rutten (Feb 25 2019 at 12:09):
Hi @Gabriel Bezerra, looks like you found an error in the official snapshots.
For comparison, here's a fragment from an Observation snapshot, generated by the (R4) FHIR .NET API:
<element id="Observation.referenceRange.id">
<path value="Observation.referenceRange.id" />
<representation value="xmlAttr" />
<short value="Unique id for inter-element referencing" />
<definition value="Unique id for the element within a resource (for internal references). This may be any string value that does not contain spaces." />
<min value="0" />
<max value="1" />
<base>
<path value="Element.id" />
<min value="0" />
<max value="1" />
</base>
<type>
<code>
<extension url="http://hl7.org/fhir/StructureDefinition/structuredefinition-json-type">
<valueString value="string" />
</extension>
<extension url="http://hl7.org/fhir/StructureDefinition/structuredefinition-xml-type">
<valueString value="xsd:string" />
</extension>
<extension url="http://hl7.org/fhir/StructureDefinition/structuredefinition-rdf-type">
<valueString value="xsd:string" />
</extension>
</code>
</type>
<mapping>
<identity value="rim" />
<map value="n/a" />
</mapping>
</element>
In this example, you can see that the particular id child element inherits all the constraints (incl. special "compiler magic" extensions) from the Element.id' ElementDefinition node in the core Element` StructureDefinition.
Gabriel Bezerra (Feb 25 2019 at 12:19):
@Michel Rutten , yes. In that case, when they disagree, which one wins?
Michel Rutten (Feb 25 2019 at 12:22):
Malformed data is ambiguous, per definition. FHIR core resource & type definitions should be completely valid. I suggest that you submit a GForge ticket to correct this.
Michel Rutten (Feb 25 2019 at 12:23):
In general, a derived profile is only allowed to further constrain the base profile; it is certainly not valid to replace an element type with another, incompatible type.
Gabriel Bezerra (Feb 25 2019 at 13:16):
Ticket submitted in GForge: https://gforge.hl7.org/gf/project/fhir/tracker/?action=TrackerItemEdit&tracker_item_id=20465
Grahame Grieve (Feb 25 2019 at 23:23):
I'll add it to my list
Last updated: Apr 12 2022 at 19:14 UTC
