Create a terminology service that validates local valuesets with external codesystems

[ewoutkramer]

Create a new ITerminologyService implementation that could do a $validate for a ValueSet, even if it does not have the codesystems mentioned in the valueset. This can be done by interpreting the composition rules in the ValueSet and then translating them to $lookups on a CodeSystem, basically bridging between a ValueSet (which the external server might not have) and the CodeSystem (which the external server could have).

That was Tim's idea, and I think we can make it work in some limited, but common cases. After studying the Java source code of the terminology client, we have concluded that Grahame is doing the same thing, in a very limited (but useful) way. We could copy that approach.

[tmprd]

Example Resource Instance snippet:

<diagnosis>
  <sequence value="1"/>
  <diagnosisCodeableConcept>
    <coding>
      <system value="http://hl7.org/fhir/sid/icd-10-cm"/>
      <code value="S06.0X1A"/>
    </coding>
  </diagnosisCodeableConcept>
  <type>
    <coding>
      <system value="http://terminology.hl7.org/CodeSystem/ex-diagnosistype"/>
      <code value="principal"/>
    </coding>
  </type>
</diagnosis>

Example Profile snippet:

<element id="ExplanationOfBenefit.diagnosis.diagnosis[x]">
  <path value="ExplanationOfBenefit.diagnosis.diagnosis[x]"/>
  <type>
    <code value="CodeableConcept"/>
  </type>
  <mustSupport value="true"/>
  <binding>
    <strength value="required"/>
    <valueSet value="http://hl7.org/fhir/us/carin-bb/ValueSet/CDCICD910CMDiagnosisCodes"/>
  </binding>
</element>

Example ValueSet snippet:

<compose>
  <include>
    <system value="http://hl7.org/fhir/sid/icd-10-cm"/>
  </include>
  <include>
    <system value="http://terminology.hl7.org/CodeSystem/icd9"/>
  </include>
</compose>

Example CodeSystem snippet (when using a local but incomplete version):

<content value="not-present"/>

Proposed Solution

• Use $validate-code with all CodeSystems in the ValueSet compose.include that we don't have locally, OR are locally available but marked as "not-present" in the CodeSystem, like this: https://tx.fhir.org/r4/CodeSystem/$validate-code?system=http://hl7.org/fhir/sid/icd-10-cm&code=S06.0X1A where this terminology server has the full CodeSystem.
• This example code will return true for the ICD-10 CodeSystem and false for the ICD-9 CodeSystem.
• Interpret this as an OR because the value is in the union of these, so the result is true (valid).