FHIR Chat · QA error on type slicing · IG creation

Stream: IG creation

Topic: QA error on type slicing

view this post on Zulip Stefan Karl (Aug 16 2018 at 11:02):

I'm getting QA errors with type slicing in this profile, which restricts Observation.value[x] to valueQuantity or valueRatio and makes constraints on each of them. Here is the relevant part of StructureDefinition.differential:

    <element id="Observation.value[x]">
      <path value="Observation.value[x]"/>
      <slicing>
        <discriminator>
          <type value="type"/>
          <path value="$this"/>
        </discriminator>
        <rules value="open"/>
      </slicing>
      <min value="0"/>
      <max value="1"/>
      <type>
        <code value="Quantity"/>
      </type>
      <type>
        <code value="Ratio"/>
      </type>
      <condition value="pocd-obs-1"/>
    </element>
    <element id="Observation.value[x]:valueQuantity">
      <path value="Observation.valueQuantity"/>
      <sliceName value="valueQuantity"/>
      <type>
        <code value="Quantity"/>
      </type>
    </element>
    <element id="Observation.value[x]:valueQuantity.value">
      <path value="Observation.valueQuantity.value"/>
      <min value="1"/>
    </element>
    <element id="Observation.value[x]:valueQuantity.system">
      <path value="Observation.valueQuantity.system"/>
      <fixedUri value="http://unitsofmeasure.org"/>
    </element>
    <element id="Observation.value[x]:valueRatio">
      <path value="Observation.valueRatio"/>
      <sliceName value="valueRatio"/>
      <type>
        <code value="Ratio"/>
      </type>
    </element>
    <element id="Observation.value[x]:valueRatio.numerator">
      <path value="Observation.valueRatio.numerator"/>
    </element>
    <element id="Observation.value[x]:valueRatio.numerator.value">
      <path value="Observation.valueRatio.numerator.value"/>
      <min value="1"/>
    </element>
    <element id="Observation.value[x]:valueRatio.numerator.system">
      <path value="Observation.valueRatio.numerator.system"/>
      <fixedUri value="http://unitsofmeasure.org"/>
    </element>
    <element id="Observation.value[x]:valueRatio.denominator">
      <path value="Observation.valueRatio.denominator"/>
    </element>
    <element id="Observation.value[x]:valueRatio.denominator.value">
      <path value="Observation.valueRatio.denominator.value"/>
      <min value="1"/>
    </element>
    <element id="Observation.value[x]:valueRatio.denominator.system">
      <path value="Observation.valueRatio.denominator.system"/>
      <fixedUri value="http://unitsofmeasure.org"/>
    </element>

This example referencing the profile gets an "Element matches more than one slice" error. What's going wrong here?

view this post on Zulip Grahame Grieve (Aug 16 2018 at 11:03):

I don't know. is it committed?

view this post on Zulip Stefan Karl (Aug 16 2018 at 11:08):

It's in the PoCD Implementation Guide.

view this post on Zulip Grahame Grieve (Aug 16 2018 at 11:10):

ok I'll add it to my list

view this post on Zulip Stefan Karl (Aug 16 2018 at 11:11):

Thanks

view this post on Zulip Grahame Grieve (Aug 17 2018 at 00:28):

@Lloyd McKenzie I'm not sure what to do with this one. The goal is to constrain a 0..1 element with a choice of types to a single type, and then constrain it.

view this post on Zulip Grahame Grieve (Aug 17 2018 at 00:29):

http://build.fhir.org/elementdefinition.html#slicing says:
Elements that allow a choice of multiple types can be constrained. In principle, there are two different types of constraints to apply:

  • A constraint that applies to the element as a whole - e.g. as restricting the cardinality, or limiting the choice of types
  • A constraint that applies to the use of a particular type - e.g. value set binding

When constraining elements with multiple types, the following rules apply:

  • Constraints limiting the acceptable list of types must be applied to the original "[x]" element as this is where the list of acceptable types is defined
  • The inclusion of a type specific path (such as "Patient.deceasedBoolean") SHALL NOT be interpreted as constraining allowed types, but instead, it constrains the use of a particular type
  • the original element SHALL always be represented in a snapshot; the type specific variants are only represented when needed

view this post on Zulip Grahame Grieve (Aug 17 2018 at 00:31):

so I would expect that you'd have this:
Observation.value[x]
type = Quantity
Observation.valueQuantity
Observation.valueQuantity.system
fixedUri = http://unitsofmeasure.org

view this post on Zulip Grahame Grieve (Aug 17 2018 at 00:31):

but the snapshot generator doesn't accept this. Where as the validator seems to assume it...

view this post on Zulip Lloyd McKenzie (Aug 17 2018 at 00:50):

Agree that the snapshot generator should allow/expect this. Also realize that digging into that particular piece of code at this point in the process is a very scary prospect...

view this post on Zulip Grahame Grieve (Aug 17 2018 at 00:53):

Yes @Stefan Karl we're going to carry this error. We'll fix it after ballot

Last updated: Apr 12 2022 at 19:14 UTC


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