Proposed Wording: Table of strength showing binding in base resources in rows against strength on derived profiles in columns. This table shows what override in derived profiles is allowed and what is not allowed.

Additional URL: http://hl7.org/fhir/2015May/terminologies.html#1.23.0.2

Expl Pref'd Ext Req

Example - O O O

Preferred X - O O

Extensible X X - O

Required X X X -

Legend:

X = override not allowed

O = override allowed

• = uses same strength (no change)

Comment:

If domain resource has strength=required on the binding then derived profiles cannot loosen the strength to extensible, though you can reduce the number of codes in the value set.

This is not clearly defined in the FHIR spec in section 2.14.0.1 resulting in some profiles that break the rules.

At least 3 HL7 FHIR profiles are defined with binding=extensible on bindings declared as required in the base resource.

For example, the snapshot view for daf-diagnosticorder profile with element DiagnosticOrder.item.code shows binding as being overridden which should not be allowed.

<binding>

<name value="USLabObservationName"/>

<strength value="extensible"/>

<description value="LOINC codes"/>

<valueSetReference>

<reference value="http://hl7.org/fhir/vs/obs-uslab-codes"/>

</valueSetReference>

</binding>

1. DiagnosticOrder.item.code

DiagnosticRequests* Required* http://hl7.org/fhir/vs/diagnostic-requests* (base)

USLabObservationName Extensible http://hl7.org/fhir/vs/obs-uslab-codes

2. DiagnosticReport.name

DiagnosticReportNames* Required* http://hl7.org/fhir/vs/report-names* (base)

USLabObservationName Extensible http://hl7.org/fhir/vs/obs-uslab-codes

3.Encounter.hospitalization.dischargeDisposition

DischargeDisp* Required* http://hl7.org/fhir/vs/encounter-discharge-disposition* (base)

DAFDischargeDispo Extensible http://hl7.org/fhir/vs/daf-encounter-dischargedisposition