Stream: implementers
Topic: Can / should an Extension.url contain an optional version?
John Timm (Jul 21 2020 at 15:42):
The spec mentions resolving the StructureDefinition for an extension using a "canonical" URL though Extension.url is typed to uri. Can / should Extension.url be used in a similar fashion to Resource.meta.profile where an optional version can be appended?
"The url SHALL be a URL, not a URN (e.g. not an OID or a UUID), and it SHALL be the canonical URL of a StructureDefinition that defines the extension. Except for child extensions defined within complex extensions, the URL SHALL be an absolute URL."
When I think of a canonical URL, I think about the potential for an optional version (especially if we are looking up a StructureDefinition from a registry).
Lloyd McKenzie (Jul 21 2020 at 16:00):
Extension.url is not allowed to contain "|version" because it does not have a type of canonical. This is intentional.
John Timm (Jul 21 2020 at 16:02):
So perhaps the wording should be changed to not include "canonical URL"?
Lloyd McKenzie (Jul 21 2020 at 16:04):
It's a reference to the canonical URL, but it's not of type 'canonical'.
John Timm (Jul 21 2020 at 16:13):
Perhaps the language should then be changed from SHALL be the canonical URL of a StructureDefinition that defines the extension to SHALL be a reference to the canonical URL of a StructureDefinition that defines the extension though the nuance between an element of type canonical and a reference to a canonical URL still seems a bit ambiguous to me.
Lee Surprenant (Jul 21 2020 at 16:18):
Extension.url is not allowed to contain "|version" because it does not have a type of canonical. This is intentional.
Mind expanding on the intention behind this? Elsewhere, when we have a reference to a definitional knowledge artifact that needs to get looked up, it tends to be a canonical (so that it can include the version), right? Why not here?
Lloyd McKenzie (Jul 21 2020 at 17:13):
@Grahame Grieve
Grahame Grieve (Jul 21 2020 at 21:29):
it's deliberate because you should not change the definition of an extension so much that the version becomes relevant to the interpretation
Grahame Grieve (Jul 21 2020 at 21:29):
but I do think that it's reasonable to clarify the language
Lloyd McKenzie (Jul 22 2020 at 05:04):
@John Timm Can you submit a change request asking for the clarification?
John Timm (Jul 24 2020 at 20:34):
Created: https://jira.hl7.org/browse/FHIR-28143
Last updated: Apr 12 2022 at 19:14 UTC
