Stream: fhir/infrastructure-wg
Topic: Fixed value on Extension URL
Matthijs van der Wielen (Sep 02 2020 at 10:32):
When an extension is added to a profile, the url for that extension becomes a fixed value, so canonical versioning in extension urls is not allowed.
The only thing we were able to find about this in the spec is that the URL of the extension (https://www.hl7.org/fhir/extensibility-definitions.html#Extension.url) is of type uri and not of type canonical. So | has no special meaning.
When the derived profile states:
<element id="Patient.extension:birthPlace">
<path value="Patient.extension" />
<sliceName value="birthPlace" />
<min value="1" />
<type>
<code value="Extension" />
<profile value="http://hl7.org/fhir/StructureDefinition/patient-birthPlace" />
</type>
</element>
An instance can't say that it wants to use a specific version of that extension like this:
<extension url="http://hl7.org/fhir/StructureDefinition/patient-birthPlace|4.0.1">
<valueAddress>
<text value="MakeUpStreet 845" />
</valueAddress>
The instance literally refers to the extension with the set uri, so the extension uri with |4.0.1 added is not valid.
Can a case be made that the spec can say something like: "Fixed" values for canonicals could be treated as "somewhat fixed"?
Grahame Grieve (Sep 02 2020 at 10:37):
This is deliberately different; the meaning of the extension must be established by a version-less reference to the extension. If the extension changes so that this is not enough, it's time for a different extension.
Grahame Grieve (Sep 02 2020 at 10:38):
but you can version a reference to an extension in the profile when you reference it, as you you show. So for validation purposes, you be specific about which versions.
Matthijs van der Wielen (Sep 02 2020 at 13:13):
Thank you @Grahame Grieve ,
Would this mean that the validator would need to infer the correct version from the profile?
Grahame Grieve (Sep 02 2020 at 13:13):
it will when validating, yes
Maximilian Reith (Sep 03 2020 at 05:09):
@Matthijs van der Wielen Thank you for checking this
Last updated: Apr 12 2022 at 19:14 UTC
