Stream: fhirpath
Topic: FHIR.Quantity versus System.Quantity
John Timm (Nov 13 2019 at 15:13):
The FHIR spec mentions the implicit conversion between FHIR.Quantity and System.Quantity including how to handle time-valued UCUM units:
http://hl7.org/fhir/fhirpath.html#quantity
but doesn't say much about how to compare quantities if they are not UCUM-based. How should a FHIRPath evaluation engine handle comparisons between two FHIR.Quantity nodes that are not UCUM quantities (either they have a code from a system other than UCUM or they do not use system/code and only unit)?
Bryn Rhodes (Nov 13 2019 at 15:51):
FHIRPath requires that quantities be either UCUM units, or a calendar duration unit: http://build.fhir.org/ig/HL7/FHIRPath/branches/master/N1/#quantity
Bryn Rhodes (Nov 13 2019 at 15:53):
So if you wanted to deal with a Quantity value in FHIR that wasn't UCUM-coded, then you would have to either convert that to a UCUM unit (so it could be represented as a System.Quantity) or deal with it specifically as a FHIR.Quantity (i.e. doing the unit and value comparisons directly, rather than treating it as a quantity).
Lee Surprenant (Nov 13 2019 at 17:10):
Should https://build.fhir.org/fhirpath.html#types or https://build.fhir.org/fhirpath.html#quantity cover the expected behavior in this case? What do the various implementations do? Seems a bit under-specified...
Grahame Grieve (Nov 13 2019 at 20:32):
what could we specify?
Lee Surprenant (Nov 13 2019 at 22:09):
That two FHIR_Quantity are comparable if they have the same coded units (even if those units aren't UCUM)?
Grahame Grieve (Nov 13 2019 at 22:10):
yeah I guess we could do that. do you want to make a task?
Lee Surprenant (Nov 13 2019 at 22:10):
sure
Lee Surprenant (Nov 13 2019 at 22:36):
ok, i submitted https://gforge.hl7.org/gf/project/fhir/tracker/?action=TrackerItemEdit&tracker_item_id=25216
Bryn Rhodes (Nov 14 2019 at 22:55):
I think for equality and equivalence, the definition follows from equality and equivalence for objects.
Bryn Rhodes (Nov 14 2019 at 22:56):
From the perspective of FHIRPath, a FHIR.Quantity is a complex object, so the standard = and ~ operators apply.
Last updated: Apr 12 2022 at 19:14 UTC
