AU Core Implementation Guide
3.0.0-ballot1 - Ballot

AU Core Implementation Guide - Downloaded Version 3.0.0-ballot1 See the Directory of published versions

## General Requirements

Page standards status: Informative

### Conforming to AU Core

There are two different ways to implement AU Core:

1. Profile Only Support: system that represents digital health information using AU Core profiles without the expectation to implement any FHIR specified interactions.
2. Profile Support + Interaction Support: system that represents digital health information using AU Core profiles (Profile Support) AND implements the FHIR REST API interactions defined by an AU Core Capability Statement (Interaction Support).

The requirements of the FHIR standard and FHIR Conformance Rules apply, and define the use of terms in this guide including the conformance verbs - SHALL, SHALL NOT, SHOULD, SHOULD NOT, MAY.

Implementers are advised to be familiar with the requirements of the FHIR standard when implementing AU Core, in particular:

- FHIR Terminology requirements
- FHIR RESTful API
- FHIR Search
- FHIR Resource formats
- FHIR Data Types

### Conformance Artifacts

#### AU Core Profiles and Extensions

The Profiles and Extensions page lists the AU Core profiles and AU Core extensions defined for this implementation guide. An AU Core profile StructureDefinition defines the minimum elements, extensions, vocabularies and value sets that SHALL be present and constrains the way elements are used when conforming to the profile.

AU Core profile elements include mandatory and Must Support requirements. Mandatory Elements are required and have a minimum cardinality > 0. Must Support elements have defined conformance obligations in AU Core based on actor roles.

Systems may implement AU Core as:

- Profile Only Support for a system declaring conformance to one or more AU Core profiles
- Profile Support + Interaction Support for a system declaring conformance to one or both of the AU Core Capability Statements

#### AU Core Capability Statements

The AU Core Requester CapabilityStatement defines the conformance requirements and expectations of an AU Core Requester actor responsible for initiating queries for information from an AU Core Responder. The complete list of FHIR profiles, REST API interactions, and search parameters that can be implemented by an AU Core Requester are defined in this capability statement.

The AU Core Responder CapabilityStatement defines the conformance requirements and expectations of an AU Core Responder actor responsible for providing responses to queries submitted by an AU Core Requester. The complete list of FHIR profiles, REST API interactions, and search parameters that can be implemented by an AU Core Responder are defined in this capability statement. An AU Core Responder declares conformance to this list of capabilities based on the resource types and interactions it implements.

#### Profile Only Support

A system that represents digital health information using the content models of AU Core profiles without the expectation to implement any AU Core interactions can declare Profile Only Support to one or more AU Core profiles.

A system that declares conformance as Profile Only Support to an AU Core profile:

- SHALL correctly populate a resource with all mandatory elements specified in the profile’s definition.
- SHALL correctly populate a resource with all Must Support elements for which a value is known.
- SHALL implement the requirements on Missing Data when an element value is not known.

A system is not required to declare Profile Only Support to all AU Core profiles. For example, a pathology laboratory system that implements the AU Core Pathology Result Observation profile, is not required to produce a MedicationRequest resource.

#### Profile Support + Interaction Support

Profile Support + Interaction Support refers to a system that represents digital health information using the content models of AU Core profiles AND implement the REST API interactions defined by the applicable AU Core capability statement.

An AU Core Responder that declares Profile Support + Interaction Support conformance:

- SHALL declare conformance to the AU Core Responder Capability Statement in the server's CapabilityStatement.
- SHALL specify the implemented resource types, associated AU Core profiles, REST API interactions and search parameters in the server's CapabilityStatement.
- SHALL implement the mandatory and/or Must Support requirements for the elements defined as such in the implemented AU Core profiles.
- SHALL implement the required REST API interactions and search parameters as defined in the AU Core Responder Capability Statement.

An AU Core Requester that declares Profile Support + Interaction Support conformance:

- SHALL implement the mandatory and/or Must Support requirements for the elements defined as such in the implemented AU Core profiles.
- SHALL implement the required REST API interactions and search parameters as defined in the AU Core Requester Capability Statement.

### Mandatory Elements

Mandatory elements are elements with minimum cardinality > 0. When an element is mandatory, the data is expected to always be present. Very rarely, it may not be, and in this circumstance the requirements in Missing Data SHALL be applied. An element can be both Must Support and mandatory, in which case the requirements for mandatory's Missing Data requirements apply as described in Missing Must Support and Mandatory Data.

The convention in this guide is to mark all mandatory elements as Must Support unless they are nested under an optional element.

### Must Support and Obligation

Labelling an element Must Support means that systems that produce or consume resources SHALL provide support for the element in some meaningful way. The FHIR standard does not define exactly what 'meaningful' support for an element means, but indicates that a profile SHALL make clear exactly what kind of support is required when an element is labelled as Must Support.

Because AU Core is a foundational standard, Must Support needs to be defined in a way that does not impede or prescribe what a system does with the data, so as not to impede each implementation’s ability to tighten and define expectations for use under their own business rules, regulations, policies, etc. There is also a challenge that comes from inheritance of Must Support flags into implementation guides that have strict definitions for Must Support (e.g., must be able to display this value to an end user). AU Core will only apply the Must Support flag on the elements that are necessary to support minimum requirements and are expected to be flagged as Must Support across the majority of Australian FHIR implementation guides.

In AU Core, the meaning of Must Support is specified in terms of Obligation Codes in obligation extensions on the element definition. These obligations can also be applied at more granular levels, such as individual data type choices, terminology bindings, identifiers, or sub-elements. The obligation codes used to define the minimum obligations of Must Support elements in this implementation guide are reiterated below.

Must Support on a profile element SHALL be interpreted as detailed in the Interpreting Profile Elements Labelled Must Support section, which includes additional narrative conformance requirements where agreed.

Actor | Code | Display | Definition | Notes
--- | --- | --- | --- | ---
AU Core Responder | SHALL:populate-if-known | SHALL populate if known | Conformant applications producing resources SHALL correctly populate this element if they know a value for the element, but it is acceptable if the system is unable to ever know a value for the element. | This obligation does not impose a requirement to be able to know a value, unlike populate and able-to-populate which do. 'Knowing' an element means that a value for the element is available in memory, persistent store, or is otherwise available within the system claiming conformance.
AU Core Responder | SHOULD:populate | SHOULD populate | Conformant applications producing resources SHOULD include this element if a value is known and allowed to be shared. | This implementation obligation means that whenever the producer knows the correct value for an element, it should populate it. This is NOT the same as cardinality, as a 'populate' element can be omitted if no data exists or the data that exists is prohibited from being shared. Organizations might be required to formally document their rules for determining when they are 'able to share' as part of conformance testing processes. (e.g. regulatory, consent, etc.)
AU Core Requester | SHALL:no-error | SHALL not error if present | Conformant applications SHALL accept resources containing any valid value for the element without error. | Applications are still able to inform the user that a value cannot be processed correctly and may ignore the data, but applications aren't able to reject an instance merely because the element is present (which would be allowed for elements that do not have this obligation). A system MAY raise an error if the value provided is not valid or violates specific business rules. This obligation also applies to elements that only contain an extension in place of a value where (or equivalent), should either of these be allowed on the consumer obligations

Must Support elements are treated differently between AU Core Responder and AU Core Requester actors.

#### AU Core Responder

An AU Core Responder:

- SHALL correctly populate all Must Support elements for which a value is known.
- SHALL implement the requirements on Suppressed Data when an element is NOT allowed to be shared.
- SHALL implement the requirements on Missing Data when an element value is not known.

When a Must Support element requires additional or stronger obligation, this obligation is specified in the AU Core Responder obligation extension on the element definition.

#### AU Core Requester

An AU Core Requester:

- SHALL accept resources containing any valid value for Must Support elements without error.
- SHALL accept resources containing Must Support elements with Missing Data or Suppressed Data without error.

How the system processes the resource depends on local requirements that could align with obligation terms such as reject invalid, correctly handle, persist, display, or ignore.

When a Must Support element requires additional or stronger obligation, this obligation is specified in the AU Core Requester obligation extension on the element definition.

#### Presentation of Must Support and Obligation in Profiles

All elements with Must Support in AU Core are accompanied by an explicit obligation that identifies the expectations for one or more actors. When rendered in an implementation guide, each profile is presented in different formal views under tabs labelled "Differential Table", "Key Elements Table", and "Snapshot Table". Elements flagged with Must Support and stated obligations in these views are represented by S O as shown below.

Figure 1: Key Elements Table View

Implementers need to refer to the "Key Elements Table" (or the "Snapshot Table") to see the full set of elements that are mandatory or Must Support with obligations, terminology requirements and constraints (i.e. invariants).

##### Presentation of Must Support and Obligation in Raw Representations

When viewing the raw representation (e.g. XML or JSON) of a profile, elements with Must Support are denoted by `mustSupport` set to "true", and obligations are defined in the Obligation Extension as shown in the example below.

Example: AU Core AllergyIntolerance profile with Must Support and obligations on clinicalStatus.

    {
        "resourceType" : "StructureDefinition",
        ...
        "url" : "http://hl7.org.au/fhir/core/StructureDefinition/au-core-allergyintolerance",
        ...
               {
                  "id" : "AllergyIntolerance.clinicalStatus",
                  "extension" : [{
                    "extension" : [{
                    "url" : "code",
                    "valueCode" : "SHALL:populate-if-known"
                },
                {
                    "url" : "actor",
                    "valueCanonical" : "http://hl7.org.au/fhir/core/ActorDefinition/au-core-actor-responder"
                }],
                "url" : "http://hl7.org/fhir/StructureDefinition/obligation"
                },
                {
                    "extension" : [{
                    "url" : "code",
                    "valueCode" : "SHALL:no-error"
                },
                {
                    "url" : "actor",
                    "valueCanonical" : "http://hl7.org.au/fhir/core/ActorDefinition/au-core-actor-requester"
                  }],
                "url" : "http://hl7.org/fhir/StructureDefinition/obligation"
                }],
                "path" : "AllergyIntolerance.clinicalStatus",
                "mustSupport" : true,
               },
        ...
    }

#### Interpreting Profile Elements Labelled Must Support

The section is provided as additional support in understanding of Must Support and obligations on elements in AU Core. This section does not override the obligations defined for an actor - implementers also need to read the profile specific implementation guidance for any qualifying requirements placed on the obligations for a Must Support element.

Profiles defined in this implementation guide flag Must Support on elements (e.g. `Patient.name`) and sub-elements of a data type (e.g. `Patient.name.use`). The explanation on how to interpret Must Support for an element does not address rules defined in each profile - which may limit or extend what is allowed for each element. For example, the profile AU Core Patient limits what is considered valid for the element `Patient.name` with the invariant "au-core-pat-02: At least one patient name shall have a family name".

##### Must Support - Primitive Elements

Primitive elements are single elements with a primitive value. If a primitive element is labelled as Must Support:

- AU Core Responders SHALL correctly populate the element if a value is known.
- AU Core Requesters SHALL accept resources without error if the element is present and contains any valid value.

For example, the AU Core Organization Profile `Organization.name` element is a primitive string datatype. Therefore, when claiming conformance to this profile:

- AU Core Responders SHALL correctly populate a value in `Organization.name` if a value is known.
- AU Core Requesters SHALL accept the Organization resource without error if `Organization.name` is present and contains any valid value.

##### Must Support - Complex Elements

Complex elements are composed of primitive and other complex elements. Elements may have additional rules defined in the profile that also apply, e.g. invariants. Coded elements (CodeableConcept, Coding, and code datatypes) have additional rules defined by the terminology binding in the profile.

If a complex element is labelled as Must Support:

- AU Core Responders SHALL correctly populate the element with at least one of the sub-element values if the value is known.
- AU Core Requesters SHALL accept resources without error if the element is present and contains any valid sub-element.

For example, the AU Core AllergyIntolerance Profile `AllergyIntolerance.note` element is labelled Must Support and has no Must Support sub-elements. When claiming conformance to this profile:

- AU Core Responders SHALL correctly populate a value in any valid `AllergyIntolerance.note` sub-element if a value is known e.g. `AllergyIntolerance.note.text`.
- AU Core Requesters SHALL accept the AllergyIntolerance resource without error if `AllergyIntolerance.note` is present and contains any valid sub-elements.

If a sub-element is labelled as Must Support:

- AU Core Responders SHALL correctly populate the element with all Must Support sub-elements for which a value is known.
- AU Core Requesters SHALL accept resources without error if Must Support sub-elements are present and contains any valid value.

For example, in the AU Core Practitioner Profile, the `Practitioner.name` element is labelled Must Support and has Must Support sub-elements `Practitioner.name.family` and `Practitioner.name.given`. When claiming conformance to this profile:

- AU Core Responders SHALL correctly populate a value in `Practitioner.name.family` and `Practitioner.name.given` if the value for those sub-elements is known.
- AU Core Requesters SHALL accept a Practitioner resource without error if `Practitioner.name` is present and contains valid values in `Practitioner.name.family` and `Practitioner.name.given` sub-elements.

##### Must Support - Resource References

Some elements labelled as Must Support reference multiple resource types or profiles such as `Observation.performer`. In such cases:

- AU Core Responders SHALL correctly populate the element with at least one referenced resource or allowed profile if the value is known.
- AU Core Requesters SHALL accept resources without error if the element is present and contains any valid referenced resource or profile.

The table below provides a list of AU Core profile elements that allow multiple referenced resource types or profiles.

AU Core Profile | Must Support Element | Reference
--- | --- | ---
AU Core Composition | Composition.author | Device, AU Core Organization, AU Core Patient, AU Core Practitioner, AU Core PractitionerRole, AU Core RelatedPerson
AU Core Composition | Composition.attester.party | AU Core Organization, AU Core Patient, AU Core Practitioner, AU Core PractitionerRole, AU Core RelatedPerson
AU Core Diagnostic Result Observation | Observation.performer | AU Core Practitioner, AU Core PractitionerRole, AU Core Organization, AU Core Patient, AU Core RelatedPerson
AU Core Diagnostic Result Observation | Observation.hasMember | AU Base Diagnostic Imaging Result, AU Core Diagnostic Result Observation, AU Core Pathology Result Observation
AU Core DiagnosticReport | DiagnosticReport.performer | CareTeam, AU Core Organization, AU Core Practitioner, AU Core PractitionerRole
AU Core DiagnosticReport | DiagnosticReport.result | AU Base Diagnostic Imaging Result, AU Core Diagnostic Result Observation, AU Core Pathology Result Observation
AU Core DocumentReference | DocumentReference.author | AU Core Practitioner, AU Core PractitionerRole, AU Core Patient, AU Core RelatedPerson, AU Core Organization, Device
AU Core Encounter | Encounter.participant.individual | AU Core Practitioner, AU Core PractitionerRole, AU Core RelatedPerson
AU Core Encounter | Encounter.reasonReference | AU Core Condition, Observation, AU Core Procedure
AU Core MedicationDispense | MedicationDispense.performer.actor | Device, AU Core Organization, AU Core Patient, AU Core Practitioner, AU Core PractitionerRole, AU Core RelatedPerson
AU Core MedicationRequest | MedicationRequest.requester | AU Core Practitioner, AU Core PractitionerRole, AU Core Organization, AU Core Patient, AU Core RelatedPerson
AU Core MedicationRequest | MedicationRequest.reasonReference | AU Core Condition, Observation
AU Core MedicationStatement | MedicationStatement.reasonReference | AU Core Condition, AU Core DiagnosticReport, Observation
AU Core Pathology Result Observation | Observation.performer | AU Core Practitioner, AU Core PractitionerRole, AU Core Organization, AU Core Patient, AU Core RelatedPerson
AU Core Procedure | Procedure.reasonReference | AU Core Condition, Observation, AU Core Procedure, AU Core DocumentReference

##### Must Support - Choice of Data Types

Some elements labelled as Must Support allow different data types such as `Observation.effective[x]`. In such cases:

- AU Core Responders SHALL correctly populate the element with at least one data type allowed by the element definition if the value is known.
- AU Core Requesters SHALL accept resources without error if the element is present and contains any valid data type allowed by the element definition.

The table below provides a list of AU Core profile elements that allow multiple data types.

AU Core Profile | Must Support Element | Data Types
--- | --- | ---
AU Core AllergyIntolerance | AllergyIntolerance.onset[x] | dateTime, Age, Period, Range
AU Core Condition | Condition.onset[x] | dateTime, Age, Period, Range
AU Core Condition | Condition.abatement[x] | dateTime, Age, Period, Range
AU Core DiagnosticReport | DiagnosticReport.effective[x] | dateTime, Period
AU Core Diagnostic Result Observation | Observation.effective[x] | dateTime, Period, Timing, instant
AU Core Pathology Result Observation | Observation.effective[x] | dateTime, Period, Timing, instant
AU Core Diagnostic Result Observation | Observation.value[x] | Quantity, CodeableConcept, string, boolean, integer, Range, Ratio, SampledData, time, dateTime, Period
AU Core Pathology Result Observation | Observation.value[x] | Quantity, CodeableConcept, string, boolean, integer, Range, Ratio, SampledData, time, dateTime, Period
AU Core Diagnostic Result Observation | Observation.component.value[x] | Quantity, CodeableConcept, string, boolean, integer, Range, Ratio, SampledData, time, dateTime, Period
AU Core Immunization | Immunization.occurrence[x] | dateTime, string
AU Core MedicationRequest | MedicationRequest.medication[x] | CodeableConcept, Reference
AU Core MedicationStatement | MedicationStatement.medication[x] | CodeableConcept, Reference
AU Core MedicationStatement | MedicationStatement.effective[x] | dateTime, Period
AU Core Pathology Result Observation | Observation.component.value[x] | Quantity, CodeableConcept, string, boolean, integer, Range, Ratio, SampledData, time, dateTime, Period
AU Core Procedure | Procedure.performed[x] | dateTime, Period, string, Age, Range
AU Core Blood Pressure | Observation.component.value[x] | Quantity, CodeableConcept, string, boolean, integer, Range, Ratio, SampledData, time, dateTime, Period
AU Core Body Height | Observation.component.value[x] | Quantity, CodeableConcept, string, boolean, integer, Range, Ratio, SampledData, time, dateTime, Period
AU Core Body Temperature | Observation.component.value[x] | Quantity, CodeableConcept, string, boolean, integer, Range, Ratio, SampledData, time, dateTime, Period
AU Core Body Weight | Observation.component.value[x] | Quantity, CodeableConcept, string, boolean, integer, Range, Ratio, SampledData, time, dateTime, Period
AU Core Heart Rate | Observation.component.value[x] | Quantity, CodeableConcept, string, boolean, integer, Range, Ratio, SampledData, time, dateTime, Period
AU Core Respiration Rate | Observation.component.value[x] | Quantity, CodeableConcept, string, boolean, integer, Range, Ratio, SampledData, time, dateTime, Period
AU Core Waist Circumference | Observation.component.value[x] | Quantity, CodeableConcept, string, boolean, integer, Range, Ratio, SampledData, time, dateTime, Period

In addition, some data type choices are labelled as Must Support and apply an additional obligation of SHOULD:populate for AU Core Responders. In such cases:

- AU Core Responders SHALL populate the element when the value is known and SHOULD be capable of correctly populating the element using this data type. Typically, this means that an application can demonstrate during some conformance testing process that there are some conditions under which it populates the element with a correct value of that data type.

The table below provides a list of AU Core profile elements where a data type choice is labelled as Must Support.

Profile | Must Support Data Type
--- | ---
AU Core AllergyIntolerance | AllergyIntolerance.onsetDateTime
AU Core Condition | Condition.onsetDateTime
AU Core Immunization | Immunization.occurrenceDateTime
AU Core Procedure | Procedure.performedDateTime

##### Must Support - Identifiers

A profile may define support for one, none, or many identifier types. Supported identifier types are included in a profile by slicing the identifier element and placing Must Support on each identifier slice.

Where no identifier slice is included in a profile, there is no expectation that a specific identifier type is supported and the section on Must Support - Complex Elements applies.

Where one or more identifier types are supported:

- AU Core Responders SHALL correctly populate the identifier element with identifiers from at least one supported identifier type where an identifier of that type is known, or any other identifier type when an identifier is known but it is not one of the supported identifier types.
- AU Core Requesters SHALL accept resources without error if the identifier element is present and contains any identifier type allowed by the element definition.

The table below provides a list of AU Core profile elements with one or more supported identifier types.

AU Core Profile | Must Support Element | Supported Identifiers
--- | --- | ---
AU Core Organization | Organization.identifier | HPI-O, Australian Business Number
AU Core Patient | Patient.identifier | IHI, Medicare Card Number, DVA Number
AU Core Practitioner | Practitioner.identifier | HPI-I
AU Core PractitionerRole | PractitionerRole.identifier | Medicare Provider Number

For example, the profile AU Core Organization defines support for the Healthcare Provider Identifier - Organisation (HPI-O) and Australian Business Number (ABN) identifier types as slices of `Organization.identifier` labelled with Must Support. When claiming conformance to the AU Core Organization Profile:

- AU Core Responders SHALL correctly populate `Organization.identifier` with at least one of HPI-O or ABN if known, or any other identifier type when neither HPI-O or ABN are known but some other identifier is known (e.g. NATA Accreditation Number).
- AU Core Requesters SHALL accept the Organization resource if `Organization.identifier` is present and containins any valid value. A valid value may be an HPI-O or ABN, or may be any other valid identifier type allowed by the element definition (e.g. NATA Accreditation Number).

Systems MAY support populating and accepting other identifiers, but this is not a requirement of AU Core.

##### Must Support - Choice of Profile Elements

A profile may label two elements as Must Support that are used to indicate a reason, e.g. `Encounter.reasonCode` and `Encounter.reasonReference` in the profile AU Core Encounter. In such cases:

- AU Core Responders SHALL correctly populate at least one element choice if the value is known.
- AU Core Requesters SHALL accept resources without error if any element allowed by the profile is present and contains any valid value.

The table below lists the applicable profiles and elements in AU Core.

AU Core Profile | Must Support Choice Elements
--- | ---
AU Core Encounter | Encounter.reasonCode, Encounter.reasonReference
AU Core MedicationRequest | MedicationRequest.reasonCode, MedicationRequest.reasonReference
AU Core MedicationStatement | MedicationStatement.reasonCode, MedicationStatement.reasonReference
AU Core Procedure | Procedure.reasonCode, Procedure.reasonReference

##### Must Support - Multiple Terminologies

A coded element can have support defined for one or many value sets. Coded elements that define support for more than one value set include them in a profile by slicing the Coding part of the element and placing Must Support on each value set slice. These value set slices are not intended to prevent systems from supplying only a text value.

Most coded Must Support elements in AU Core define support for one value set, which is bound to the element and no value set slice is present. For these elements, the section on Must Support - Complex Elements and the terminology binding applies.

Where multiple value sets are supported:

- AU Core Responders SHALL correctly populate the element with concepts from all supported value sets where the applicable concept is known.
- AU Core Requesters SHALL accept resources without error if the element is present and contains any valid value.

The table below lists the AU Core profile elements that define support for multiple value sets.

AU Core Profile | Must Support Sub-Element | Terminology Choices
--- | --- | ---
AU Core Immunization | Immunization.vaccineCode.coding | Australian Medicines Terminology Vaccine, Australian Immunisation Register Vaccine
AU Core Medication | Medication.code.coding | Australian Medication, PBS Item Codes
AU Core MedicationDispense | MedicationDispense.medicationCodeableConcept.coding | Australian Medication, PBS Item Codes
AU Core MedicationRequest | MedicationRequest.medicationCodeableConcept.coding | Australian Medication, PBS Item Codes
AU Core MedicationStatement | MedicationStatement.medicationCodeableConcept.coding | Australian Medication, PBS Item Codes

For example, the profile AU Core Medication defines support for Australian Medication and PBS Item Codes value sets as slices of `Medication.code.coding` labelled with Must Support.

When claiming conformance to the AU Core Medication profile:

- AU Core Responders SHALL correctly populate `Medication.code.coding` with codes from Australian Medication and PBS Item Codes if both coded values are known, or from either if only one is known, or from another terminology if neither is known but a code is available, or text only if no coded value is known.
- AU Core Requesters SHALL accept a Medication resource without error if `Medication.code.coding` is present and contains any valid value. A valid value may be text, or may be a code from Australian Medication or PBS Item Codes, or both, or some other code.

Systems MAY populate and accept concepts from other value sets but this is not a requirement of AU Core.

### Missing Data

There are situations when information for a particular data element is missing and the source system does not know the reason for the absence of data.

#### Missing Must Support and Optional Data

If the source system does not know the value for an optional element (minimum cardinality = 0), including elements labelled Must Support, the data element SHALL be omitted from the resource.

#### Missing Must Support and Mandatory Data

If the data element is a mandatory element (minimum cardinality is > 0), the element SHALL be present even if the source system does not know the value or the reason the value is absent.

1. For non-coded data elements where the applicable AU Core profile does not mandate a sub-element
   - use the DataAbsentReason extension
   - use the code "unknown": The value is expected to exist but is not known
   - For some AU Core Observation profiles the `Observation.value` element is conditionally mandatory, e.g. AU Core Body Height. In this case the `Observation.dataAbsentReason` element is used with the code "unknown" rather than the DataAbsentReason extension. Requesters are advised that other meaningful values can be captured in `Observation.dataAbsentReason` beyond missing or suppressed.

   Example: Patient resource where the patient's birthDate is not available.

       {
         "resourceType" : "Patient",
              ...
              "_birthDate" : {
                   "extension" : [
                     {
                       "url" : "http://hl7.org/fhir/StructureDefinition/data-absent-reason",
                       "valueCode" : "unknown"
                     }
                   ]
                 },
             ...
            }

2. For non-coded data elements where the applicable AU Core profile mandates a sub-element, e.g. in AU Core Practitioner, the sub-element `Practitioner.name.family` is mandatory, the resource must contain the sub-element otherwise the resource will not be conformant.

3. For coded data elements:
   - required binding strength:
     - use the appropriate "unknown" concept code from the value set if available.
     - if the value set does not have the appropriate "unknown" concept code, you must use a concept from the value set anyway. Otherwise, the instance will not be conformant.
     - For AU Core profiles, the following status elements with required binding have no appropriate "unknown" concept code:
       - `AllergyIntolerance.clinicalStatus`*
       - `Condition.clinicalStatus`*
       - `Composition.status`
       - `Composition.attester.mode`
       - `Immunization.status`

     *The clinicalStatus element is conditionally mandatory based on resource-specific constraints.

   - example, preferred, or extensible binding strengths:
     - when the system has text but no coded value, only the text sub-element is populated.
     - when there is neither text or coded value:
       - use the appropriate "unknown" concept code from the value set if available.
       - when the value set does not have an appropriate "unknown" concept code, use "unknown" from the DataAbsentReason Code System.

       Example: AllergyIntolerance resource where the manifestation is unknown.

           ...
           "reaction" : [
             {
               "manifestation" : [
                 {
                   "coding" : [
                     {
                       "system" : "http://terminology.hl7.org/CodeSystem/data-absent-reason",
                       "code" : "unknown",
                       "display" : "Unknown"
                     }
                   ]
                 }
               ]
             }
           ]
           ...

   - For some AU Core Observation profiles the `Observation.value` element is conditionally mandatory, e.g. AU Core Smoking Status. In this case the `Observation.dataAbsentReason` element is used with the code "unknown" rather than the DataAbsentReason extension. Requesters are advised that other meaningful values can be captured in `Observation.dataAbsentReason` beyond missing or suppressed.

### Suppressed Data

In some circumstances, specific pieces of data may be hidden due to security or privacy reasons.

When an element definition is optional (minimum cardinality = 0), including elements labelled Must Support:

- The element SHALL NOT be populated in the resource when a value is suppressed.

When an element definition is mandatory (minimum cardinality > 0),

- The element SHALL be correctly populated but it may exceed the data requester's access rights to know that the data is suppressed:

  - where a requester does not have access rights to know that data is suppressed use the code "unknown" from the DataAbsentReason Code System following the section on Missing Data.

    Example: Patient resource where the identifier is suppressed.

        "resourceType" : "Patient",
        ...
        "identifier" : [
          {
            "extension" : [
              {
                "url" : "http://hl7.org/fhir/StructureDefinition/data-absent-reason",
                "valueCode" : "unknown"
              }
            ]
          }
        ],
        ...

  - where a requester has the access rights to know that data is suppressed use the code "masked" from the DataAbsentReason Code System following the section on Missing Data.

    Example: Observation resource where the code is suppressed.

        {
          "resourceType" : "Observation",
          ...
          "code" : {
            "coding" : [
              {
                "system" : "http://hl7.org/fhir/StructureDefinition/data-absent-reason",
                "code" : "masked"
              }
            ]
          },
          ...
        }