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First-Class Extensions

In Aidbox there are two ways to define first-class extensions:

First-class extension as Zen profile

While FHIR uses two different ways to define core elements and extensions, zen profiles provide unified framework to describe both. Zen FHIR format offers user-defined elements or "first-class extensions". In zen profiles, you can define new attributes (elements) for existing (FHIR) resources. The example below shows how to define extensions in zen profiles.
FHIR Patient with race extension
Zen profile of Patient with race extension
resourceType: Patient
id: sample-pt
extension:
- url: http://hl7.org/fhir/us/core/StructureDefinition/us-core-race
extension:
- url: text
valueString: Asian Indian
- url: ombCategory
valueCoding:
system: urn:oid:2.16.840.1.113883.6.238
code: 2028-9
display: Asian
- url: detailed
valueCoding:
system:
code: 2029-7
display: Asian Indian
MyPatientProfile
{:zen/tags #{zen/schema zen.fhir/profile-schema}
:zen.fhir/version "0.5.0"
:zen.fhir/profileUri "urn:fhir:extension:MyPatientProfile"
:confirms #{fhir/Patient}
:type zen/map
:keys {:race
{:type zen/map
:fhir/extensionUri "http://hl7.org/fhir/us/core/StructureDefinition/us-core-race"
:require #{:text}
:keys {:ombCategory {:type zen/vector
:maxItems 5
:every {:confirms #{fhir/Coding}
:zen.fhir/value-set {:symbol omb-race-category-value-set
:strength :required}}}
:detailed {:type zen/vector
:every {:confirms #{fhir/Coding}
:zen.fhir/value-set {:symbol detailed-race-value-set
:strength :required}}}
:text {:confirms #{fhir/string}
:zen/desc "Race Text"}}}}}
Note that extension elements have :confirms to a FHIR primitive or complex type specified. Previously these were specified in the base profile schema. These :confirms and the :fhir/extensionUri are needed to allow zen FHIR <-> FHIR format transformation.

Steps to define first-class extension as zen profile:

  1. 1.
    ​Initialize zen project and add additional IGs if necessary.
  2. 2.
    Define your custom first-class extension. For syntax and more examples refer to this page.
    {ns my-zen-project
    import #{zen.fhir
    hl7-fhir-r4-core.string
    hl7-fhir-r4-core.dateTime
    hl7-fhir-r4-core.uri}
    ​
    MyPatient
    {:zen/tags #{zen/schema zen.fhir/profile-schema}
    :zen/desc "Patient resource schema with first-class extension definition examples"
    :zen.fhir/version "0.5.20"
    :confirms #{zen.fhir/Resource}
    :zen.fhir/type "Patient"
    :zen.fhir/profileUri "urn:profile:MyPatientProfile"
    :type zen/map
    :keys {:meta {:type zen/map
    :keys {:tenant-id
    {:confirms #{hl7-fhir-r4-core.string/schema}
    :zen/desc "Patient.meta.tenant-id first-class extension"
    :fhir/extensionUri "http://tenant-id-extension-url"}}}
    ​
    :form {:type zen/vector
    :zen/desc "Patient.form.[*] array first-class extension"
    :every {:confirms #{hl7-fhir-r4-core.uri/schema}
    :fhir/extensionUri "http://patient-form-url"}}
    ​
    :info {:type zen/map
    :zen/desc "Patient.info nested first-class extension"
    :fhir/extensionUri "http://patient-info"
    :keys {:registration {:confirms #{hl7-fhir-r4-core.dateTime/schema}
    :zen/desc "Patient.info.registration
    extension.url deduced from key"}
    :referral {:confirms #{hl7-fhir-r4-core.uri/schema}
    :fhir/extensionUri "http://patient-info-referral"
    :zen/desc "Patient.info.referral
    extension.url is specified"}}}}}
  3. 3.
    Fix :zen.fhir/version errors if needed
    In order to fix this error, provide IG bundle with the matching zen FHIR version.
    Error message example:
    Expected '0.5.8', got '0.4.9'
    path: [:zen.fhir/version]
  4. 4.
    Define :fhir/extensionUri property value. :fhir/extensionUri "http://tenant-id-extension-url" is an equivalent of the extensionUrl field of the Attribute resource and used to form FHIR extension.
  5. 5.
    Replace plain zen type by FHIR type in your extensions. I.e. use :confirms #{hl7-fhir-r4-core.string/schema} instead of :type zen/string.

Define new extension with Attribute

In Aidbox, you can define first-class extensions using the custom resource Attribute.
Let's create an extension definition of type Reference in the REST Console of Aidbox:
Create new extension in the Aidbox format:
PUT /Attribute/ServiceRequest.requestedOrganizationDepartment
​
description: Department in the organization that made the service request
resource: {id: ServiceRequest, resourceType: Entity}
path: [requestedOrganizationDepartment]
type: {id: Reference, resourceType: Entity}
refers:
- Organization
extensionUrl: urn:extension:requestedOrganizationDepartment
  • description - string.
    Attribute text description
  • resource - required, Reference(Entity).
    Reference to a target resource type
  • path - required, array of strings.
    Path to a new attribute location in the target resource type
  • type - Reference(Entity).
    Type of data stored in this attribute. Can be any primitive or complex type.
    If omitted, treated as BackboneElement, i.e. a complex-type object with structure defined via other Attributes relying on this attribute in their path
  • isCollection - boolean.
    Whether the attribute is a collection, i.e. if true sets attribute cardinality to ..*
  • isRequired - boolean.
    Whether the attribute is required, i.e. if true sets attribute cardinality to 1..
  • isUnique - boolean. Sets unique restriction on the attribute.
  • refers - Reference(Entity).
    Only for type=Reference. Specifies to which resourceTypes this reference can refer to
  • extensionUrl - string.
    URL which will be used to create extension element in FHIR format. If omitted, Attribute won't be transformed in FHIR format
Note: you can not use Attributes and zen profiles on the same resource at the same time

Use your extension

Now, you can create the ServiceRequest resource using the new attribute requestedOrganizationDepartment in the root of the resource:
Create resource in the Aidbox format:
PUT /ServiceRequest/servicerequest-with-aidbox-native-extensions
​
requestedOrganizationDepartment:
resourceType: Organization
display: City Hospital Neurology Department
identifier: {system: 'urn:oid:1.2.3.4.5.6.7.8', value: '456'}
category:
- coding:
- {code: '183829003',
system: 'http://snomed.info/sct',
display: "Refer for imaging"}
authoredOn: '2020-01-18T15:08:00'
resourceType: ServiceRequest
requester:
resourceType: PractitionerRole
display: Din Morgan
identifier: {value: "1760", system: 'urn:oid:1.2.3.4.5.6.7.6'}
priority: routine
status: active
intent: original-order
performer:
- resourceType: Organization
display: Aga Khan University Hospital Laboratory
identifier: {value: "1514", system: 'urn:oid:1.2.3.4.5.6.7.8'}
subject:
resourceType: Patient
display: Jack Black, 10.12.1941
identifier: {value: '2155800871000065', system: 'urn:oid:1.2.3.4.5.6.7.9'}

FHIR Format

You can get the resource in the FHIR format where our new attribute is rendered as the extension element:
Note that the URL is different:GET /fhir/ServiceRequest/
Request
Response
Get the resource in the FHIR format:
GET /fhir/ServiceRequest/servicerequest-with-aidbox-native-extensions
extension:
- url: urn:extension:requestedOrganizationDepartment
valueReference:
type: Organization
identifier: {value: '456', system: 'urn:oid:1.2.3.4.5.6.7.8'}
display: City Hospital Neurology Department
category:
- coding:
- {code: '183829003',
system: 'http://snomed.info/sct',
display: "Refer for imaging"}
meta:
lastUpdated: '2020-02-04T09:15:18.664293Z'
versionId: '32'
extension:
- {url: 'ex:createdAt', valueInstant: '2020-02-04T09:12:20.103301Z'}
authoredOn: '2020-01-18T15:08:00'
resourceType: ServiceRequest
requester:
type: PractitionerRole
identifier: {value: '1760', system: 'urn:oid:1.2.3.4.5.6.7.6'}
display: Din Morgan
priority: routine
status: active
id: servicerequest-with-aidbox-native-extensions
intent: original-order
subject:
type: Patient
identifier: {value: '2155800871000065',
system: 'urn:oid:1.2.3.4.5.6.7.9'}
display: Jack Black, 10.12.1941
performer:
- type: Organization
identifier: {value: '1514', system: 'urn:oid:1.2.3.4.5.6.7.8'}
display: Aga Khan University Hospital Laboratory

Other extension examples

Let's create an extension of type Reference and list allowed resource types (Organization in that case) in the refers property.
managingOrganization
PUT /Attribute/ServiceRequest.managingOrganization
​
resourceType: Attribute
description: Organization that made the service request
resource: {id: ServiceRequest, resourceType: Entity}
path: [managingOrganization]
id: ServiceRequest.managingOrganization
type: {id: Reference, resourceType: Entity}
refers:
- Organization
extensionUrl: urn:extension:requestedOrganization
Extension of type Coding:
paymentType
PUT /Attribute/ServiceRequest.paymentType
​
resourceType: Attribute
description: Payment type for the service request, e.g. government health insurance
id: ServiceRequest.paymentType
resource:
id: ServiceRequest
resourceType: Entity
path:
- paymentType
type:
id: Coding
resourceType: Entity
extensionUrl: urn:extension:paymentType
Create resource using these extensions:
PUT /ServiceRequest/servicerequest-with-aidbox-native-extensions
​
managingOrganization:
resourceType: Organization
display: City Hospital
identifier: {value: "123", system: 'urn:oid:1.2.3.4.5.6.7.8'}
requestedOrganizationDepartment:
resourceType: Organization
display: City Hospital Neurology Department
identifier: {system: 'urn:oid:1.2.3.4.5.6.7.8', value: '456'}
paymentType: {system: 'urn:CodeSystem:paymentType',
code: "1",
display: "Government Health Insurance"}
resourceType: ServiceRequest
status: active
intent: original-order
subject:
resourceType: Patient
display: Jack Black, 10.12.1941
identifier: {value: '2155800871000065', system: 'urn:oid:1.2.3.4.5.6.7.9'}
Request
Response
Get resource in the FHIR format:
GET /fhir/ServiceRequest/servicerequest-with-aidbox-native-extensions
resourceType: ServiceRequest
extension:
- url: urn:extension:requestedOrganization
valueReference:
type: Organization
identifier: {value: '123', system: 'urn:oid:1.2.3.4.5.6.7.8'}
display: City Hospital
- url: urn:extension:requestedOrganizationDepartment
valueReference:
type: Organization
identifier: {value: '456', system: 'urn:oid:1.2.3.4.5.6.7.8'}
display: City Hospital Neurology Department
- url: urn:extension:paymentType
valueCoding: {code: '1',
system: 'urn:CodeSystem:paymentType',
display: Government Health Insurance}
status: active
id: servicerequest-with-aidbox-native-extensions
intent: original-order
subject:
type: Patient
identifier: {value: '2155800871000065', system: 'urn:oid:1.2.3.4.5.6.7.9'}
display: Jack Black, 10.12.1941

Nested extensions

Let's create a structure of nested attributes:
performerInfo
PUT /Attribute/ServiceRequest.performerInfo
​
resourceType: Attribute
description: Information filled in by performer
resource: {id: ServiceRequest, resourceType: Entity}
path: [performerInfo]
id: ServiceRequest.performerInfo
extensionUrl: urn:extension:performerInfo
performerInfo.performedBy
PUT /Attribute/ServiceRequest.performerInfo.performedBy
​
resourceType: Attribute
description: 'Information filled in by performer: performed by ["Practitioner" "PractitionerRole" "Organization" "CareTeam" "HealthcareService" "Patient" "Device" "RelatedPerson"]'
resource: {id: ServiceRequest, resourceType: Entity}
path: [performerInfo, performedBy]
id: ServiceRequest.performerInfo.performedBy
type: {id: Reference, resourceType: Entity}
isCollection: true
refers:
- Practitioner
- PractitionerRole
- Organization
- CareTeam
- HealthcareService
- Patient
- Device
- RelatedPerson
extensionUrl: urn:extension:performerInfo.performedBy
performerInfo.actualLocationReference
PUT /Attribute/ServiceRequest.performerInfo.actualLocationReference
​
resourceType: Attribute
description: 'Information filled in by performer: actual location reference'
resource: {id: ServiceRequest, resourceType: Entity}
path: [performerInfo, actualLocationReference]
id: ServiceRequest.performerInfo.actualLocationReference
type: {id: Reference, resourceType: Entity}
isCollection: true
refers:
- Location
extensionUrl: urn:extension:performerInfo.actualLocationReference
performerInfo.requestStatus
PUT /Attribute/ServiceRequest.performerInfo.requestStatus
​
resourceType: Attribute
description: 'Information filled in by performer: request status'
resource: {id: ServiceRequest, resourceType: Entity}
path: [performerInfo, requestStatus]
id: ServiceRequest.performerInfo.requestStatus
type: {id: code, resourceType: Entity}
enum:
- draft
- new
- in-progress
- suspended
- expanded
- completed
- archive
- cancelled
extensionUrl: urn:extension:performerInfo.requestStatus
performerInfo.requestActionHistory
PUT /Attribute/ServiceRequest.performerInfo.requestActionHistory
​
resourceType: Attribute
description: 'Information filled in by performer: request action history'
resource: {id: ServiceRequest, resourceType: Entity}
path: [performerInfo, requestActionHistory]
id: ServiceRequest.performerInfo.requestActionHistory
isCollection: true
extensionUrl: urn:extension:performerInfo.requestActionHistory
performerInfo.requestActionHistory.action
PUT /Attribute/ServiceRequest.performerInfo.requestActionHistory.action
​
resourceType: Attribute
description: 'Information filled in by performer: request action history - action'
resource: {id: ServiceRequest, resourceType: Entity}
path: [performerInfo, requestActionHistory, action]
id: ServiceRequest.performerInfo.requestActionHistory.action
type: {id: string, resourceType: Entity}
extensionUrl: urn:extension:performerInfo.requestActionHistory.action
performerInfo.requestActionHistory.date
PUT /Attribute/ServiceRequest.performerInfo.requestActionHistory.date
​
resourceType: Attribute
description: 'Information filled in by performer: request action history - date'
resource: {id: ServiceRequest, resourceType: Entity}
path: [performerInfo, requestActionHistory, date]
id: ServiceRequest.performerInfo.requestActionHistory.date
type: {id: dateTime, resourceType: Entity}
extensionUrl: urn:extension:performerInfo.requestActionHistory.date
performerInfo.requestActionHistory.subject
PUT /Attribute/ServiceRequest.performerInfo.requestActionHistory.subject
​
resourceType: Attribute
description: 'Information filled in by performer: request action history - subject'
resource: {id: ServiceRequest, resourceType: Entity}
path: [performerInfo, requestActionHistory, subject]
id: ServiceRequest.performerInfo.requestActionHistory.subject
type: {id: Reference, resourceType: Entity}
extensionUrl: urn:extension:performerInfo.requestActionHistory.subject
performerInfo.requestActionHistory.note
PUT /Attribute/ServiceRequest.performerInfo.requestActionHistory.note
​
resourceType: Attribute
description: 'Information filled in by performer: request action history - note'
resource: {id: ServiceRequest, resourceType: Entity}
path: [performerInfo, requestActionHistory, note]
id: ServiceRequest.performerInfo.requestActionHistory.note
type: {id: string, resourceType: Entity}
extensionUrl: urn:extension:performerInfo.requestActionHistory.note
performerInfo.requestActionHistory.author
PUT /Attribute/ServiceRequest.performerInfo.requestActionHistory.author
​
resourceType: Attribute
description: 'Information filled in by performer: request action history - author'
resource: {id: ServiceRequest, resourceType: Entity}
path: [performerInfo, requestActionHistory, author]
id: ServiceRequest.performerInfo.requestActionHistory.author
type: {id: Reference, resourceType: Entity}
extensionUrl: urn:extension:performerInfo.requestActionHistory.author
Let's add a resource using created extensions:
Create resource in the Aidbox format:
PUT /ServiceRequest/servicerequest-with-aidbox-native-extensions
​
resourceType: ServiceRequest
performerInfo:
performedBy:
- resourceType: Organization
display: City Hospital
- resourceType: PractitionerRole
display: Mark Sloan
requestStatus: completed
requestActionHistory:
- date: '2020-01-14T12:15:22'
action: new
author: {display: Meredith Grey (Psychiatrist-narcologist), resourceType: PractitionerRole}
- date: '2020-01-14T12:15:36'
action: in-progress
author: {display: Derek Shepherd (General practitioner), resourceType: PractitionerRole}
- date: '2020-01-14T12:19:00'
action: in-progress
author: {display: Derek Shepherd (General practitioner), resourceType: PractitionerRole}
subject: {display: Mark Sloan (Dental surgeon), resourceType: PractitionerRole}
note: Referred to Dr. Mark Sloan (Dental surgeon)
- date: '2020-01-14T15:05:20'
action: meeting
author: {display: Mark Sloan (Dental surgeon), resourceType: PractitionerRole}
- date: '2020-01-14T15:22:46'
action: completed
author: {display: Mark Sloan (Dental surgeon), resourceType: PractitionerRole}
status: completed
intent: original-order
category:
- text: Telemedicine consultation referral
coding:
- {code: "TMC", system: 'urn:CodeSystem:servicerequest-category', display: "Telemedicine consultation"}
subject:
resourceType: Patient
display: Jack Black, 10.12.1941
identifier: {value: '2155800871000065', system: 'urn:oid:1.2.3.4.5.6.7.9'}
Request
Response
Get resource in the FHIR format:
GET /fhir/ServiceRequest/servicerequest-with-aidbox-native-extensions
resourceType: ServiceRequest
extension:
- url: urn:extension:performerInfo
extension:
- url: urn:extension:performerInfo.performedBy
valueReference: {display: City Hospital}
- url: urn:extension:performerInfo.performedBy
valueReference: {display: Mark Sloan}
- {url: 'urn:extension:performerInfo.requestStatus', valueCode: completed}
- url: urn:extension:performerInfo.requestActionHistory
extension:
- {url: 'urn:extension:performerInfo.requestActionHistory.date', valueDateTime: '2020-01-14T12:15:22'}
- {url: 'urn:extension:performerInfo.requestActionHistory.action', valueString: new}
- url: urn:extension:performerInfo.requestActionHistory.author
valueReference: {display: Meredith Grey (Psychiatrist-narcologist)}
- url: urn:extension:performerInfo.requestActionHistory
extension:
- {url: 'urn:extension:performerInfo.requestActionHistory.date', valueDateTime: '2020-01-14T12:15:36'}
- {url: 'urn:extension:performerInfo.requestActionHistory.action', valueString: in-progress}
- url: urn:extension:performerInfo.requestActionHistory.author
valueReference: {display: Derek Shepherd (General practitioner)}
- url: urn:extension:performerInfo.requestActionHistory
extension:
- {url: 'urn:extension:performerInfo.requestActionHistory.date', valueDateTime: '2020-01-14T12:19:00'}
- {url: 'urn:extension:performerInfo.requestActionHistory.note', valueString: Referred to Dr. Mark Sloan (Dental surgeon)}
- {url: 'urn:extension:performerInfo.requestActionHistory.action', valueString: in-progress}
- url: urn:extension:performerInfo.requestActionHistory.author
valueReference: {display: Derek Shepherd (General practitioner)}
- url: urn:extension:performerInfo.requestActionHistory.subject
valueReference: {display: Mark Sloan (Dental surgeon)}
- url: urn:extension:performerInfo.requestActionHistory
extension:
- {url: 'urn:extension:performerInfo.requestActionHistory.date', valueDateTime: '2020-01-14T15:05:20'}
- {url: 'urn:extension:performerInfo.requestActionHistory.action', valueString: meeting}
- url: urn:extension:performerInfo.requestActionHistory.author
valueReference: {display: Mark Sloan (Dental surgeon)}
- url: urn:extension:performerInfo.requestActionHistory.subject
valueReference: {display: '2020-01-08'}
- url: urn:extension:performerInfo.requestActionHistory
extension:
- {url: 'urn:extension:performerInfo.requestActionHistory.date', valueDateTime: '2020-01-14T15:22:46'}
- {url: 'urn:extension:performerInfo.requestActionHistory.action', valueString: completed}
- url: urn:extension:performerInfo.requestActionHistory.author
valueReference: {display: Mark Sloan (Dental surgeon)}
status: completed
id: servicerequest-with-aidbox-native-extensions
intent: original-order
category:
- text: Telemedicine consultation referral
coding:
- {code: TMC, system: 'urn:CodeSystem:servicerequest-category', display: Telemedicine consultation}
subject:
identifier: {value: '2155800871000065', system: 'urn:oid:1.2.3.4.5.6.7.9'}
display: Jack Black, 10.12.1941

Using FHIR extensions

FHIR extensions defined in the specification can be found in the registry http://hl7.org/fhir/extensibility-registry.html.
Let's create an attribute for the servicerequest-precondition extension:
PUT /Attribute/ServiceRequest.precondition
​
resourceType: Attribute
description: "The condition or state of the patient, prior or during
the diagnostic procedure or test, for example, fasting, at-rest,
or post-operative. This captures circumstances that may influence
the measured value and have bearing on the interpretation of the result."
resource: {id: ServiceRequest, resourceType: Entity}
path: [precondition]
id: ServiceRequest.precondition
type: {id: CodeableConcept, resourceType: Entity}
isCollection: true
extensionUrl: "http://hl7.org/fhir/StructureDefinition/servicerequest-precondition"
Let's create a resource in the FHIR format:
Create resource in the FHIR format:
PUT /fhir/ServiceRequest/servicerequest-with-aidbox-native-extensions
​
resourceType: ServiceRequest
status: active
intent: original-order
subject:
type: Patient
display: Jack Black, 10.12.1941
extension:
- url: http://hl7.org/fhir/StructureDefinition/servicerequest-precondition
valueCodeableConcept:
text: After calorie fasting
coding:
- code: "726055006"
system: http://snomed.info/sct
display: After calorie fasting
- url: http://hl7.org/fhir/StructureDefinition/servicerequest-precondition
valueCodeableConcept:
text: At rest
coding:
- code: "263678003"
system: http://snomed.info/sct
display: At rest
Let's get the resource in the Aidbox format:
Request
Response
Get resource in the Aidbox format:
GET /ServiceRequest/servicerequest-with-aidbox-native-extensions
resourceType: ServiceRequest
id: servicerequest-with-aidbox-native-extensions
intent: original-order
status: active
subject: {type: Patient, display: 'Jack Black, 10.12.1941'}
precondition:
- text: After calorie fasting
coding:
- {code: '726055006',
system: 'http://snomed.info/sct',
display: After calorie fasting}
- text: At rest
coding:
- {code: '263678003',
system: 'http://snomed.info/sct',
display: At rest}

Create FHIR primitive type extension

FHIR primitive named fieldName can be extended with _fieldName field. Aidbox treats fieldName as independent from fieldName. Aidbox do not validate fields with names started with underscore.
Suppose we need to extend Patient.gender attribute with primitive type. It means, that we need to create Patient._gender attribute.
PUT /Attribute/Patient._gender
​
path:
- _gender
resource:
id: Patient
resourceType: Entity
id: Patient._gender
resourceType: Attribute
Now we can add extension attribute into _gender attribute.
PUT /Attribute/Patient._gender.extension
​
path:
- _gender
- extension
resource:
id: Patient
resourceType: Entity
id: Patient._gender.extension
isCollection: true
type:
id: Extension
resourceType: Entity
resourceType: Attribute
Finally, add Patient with extended gender.
PUT /Patient/p-gender
​
gender: male
_gender:
extension:
- valueCodeableConcept:
coding:
- code: code-male
system: system-gender
url: https://example.com
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