Extending FHIR by Ewout Kramer

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EXTENDING FHIRINTERNATIONAL DEVDAYS 2015 – Advanced Track


FHIR extension points

Start with an empty Basic Resource Extend an existing resource or datatype

(StructureDefinition) Add additional operations or search

parameters (OperationDefinition, SearchParameter)

Publish your extensions Make your server indicate support using the

Conformance resource


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Basic Resource

As close as you can get to a “new” resource Use Basic if you need a resource and it

clearly doesn't fit one of the ones currently defined, use Basic.


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An example instance…

01. Referral Basic.xml

Note how the nested extensions are <extension> elements with “simple” urls

Yes, you could nest “real” extensions -> extensions on an extension


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Let’s define a referral

This is a complex extension on Basic

Define a complex “referral” extension (that’s a StructureDefinition)

Define a “basic-referral” profile on Basic to constrain it to use the extension (and this extension only)


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Schematic

Resource “Basic” (instance)

code: referralsubject: “Patient/f201”author: “Practitioner/example”

Extension “referral” (instance)

Requestor: “Practitioner/f101”Service:ConsultationTarget Date:April 1 - April 31Status: COMPLETED

StructureDefinition “basic-referral” (constraint)

“Must have code, subject, author”“Must have one extension “referral””

StructureDefinition “referral”(extension)

Requestor: ReferenceType: CodeableConceptTargetDate: PeriodStatus: Code

defines defines


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A simple extension

Let’s first define a simple extension with a single value “Boolean”

Note how this is a StructureDefinition = a constraint on the Extension datatype!

Fix this URL to the extension’s url

Limit to just “Boolean” [1..1]

Don’t allow nested extensions


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The simple extension

02. Referral Extension - step 1.xml

Note the contextType/context Means it can be used on Basic (no one says

it should -> we’ll handle this later) Note the root has cardinality 1..1 ->

extension cannot repeat in an instance


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The complex extension

02. Referral Extension - step 2.xml

Since these are nested <extension> elements (see the instance)…. You need to “slice” the <extension> element of Extension

(read that again) And make sure value[x] does not appear


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Schematic

Resource “Basic” (instance)

code: referralsubject: “Patient/f201”author: “Practitioner/example”

Extension “referral” (instance)

Requestor: “Practitioner/f101”Service:ConsultationTarget Date:April 1 - April 31Status: COMPLETED

StructureDefinition “basic-referral” (constraint)

“Must have code, subject, author”“Must have one extension “referral””

StructureDefinition “referral”(extension)

Requestor: ReferenceType: CodeableConceptTargetDate: PeriodStatus: Code

defines defines

√ √

√

TODO


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Constrain Basic…

Must have one extension “referral”

Fix to “referral”

Constrain to 1 Patient

No “created”


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Now mark the instance

http://hl7.org/fhir/StructureDefinition/basic-referral"


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Now, tell the world

Register extension in http://simplifier.net

Update the conformance statement of your server FHIR “metadata” operation, remember? http://spark-dstu2.furore.com/fhir/metadata

http://simplifier.net/

http://spark-dstu2.furore.com/fhir/metadata

http://spark-dstu2.furore.com/fhir/metadata


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ConformanceConformance.profile

A list of profiles that represent different use cases supported by the system.

For a server, "supported by the system" means the system hosts/produces a set of resources that are conformant to a particular profile, and allows clients that use its services to search using this profile and to find appropriate data.

GET [base]/Basic?_profile=http://hl7.org/fhir/StructureDefinition/basic-referral


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Extensions: where?

Most resources derivce from DomainResource:

Notable exceptions: Bundle, Binary


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modifierExtensions

There are some cases where the information provided in extensions modifies the meaning of the element that contains it.

If modifier extensions are present, an application cannot safely process the resource unless it knows what the extension means for its own use of the data.


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Extensions: where?

All datatypes derive from Element:

There are no modifierExtensions allowed on the basic datatypes.


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Defining search params

Now…how to search on “service” in our complex extension?


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Predefined params

For Basic:


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A “normal” param: code

05. Search Param Basic.xml

Name on the url: code (Basic?code=xxxx) Type of param: token (code is a coded type) <xpath value="f:Basic/f:code"/>


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Now for our extension

Works on “Basic”, and let’s call it “service” It’s a coded type too But it works on an extension…

06. Search Param Service.xml


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Let’s declare it in our conformance!


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Add a new param

07. Conformance with Search Param Service.xml

Uri points to the definition But that’s 0..1, you can inline some of the

definitional parts (you don’t strictly need the SearchParam resource)


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Operations…

FHIR offers the possibility to add operations on top of the standard CRUD REST interactions

Work on system/type/instance level, operations start with $<operationname>

http://fhir2.healthintersections.com.au/open/Patient/1/$everything


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Our own definition

08. OperationDefinition for trigger.xml

No parameters (nice and simple) Not idempotent Not a named query


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Let’s declare it in our conformance!


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Questions?

Extending FHIR by Ewout Kramer

Healthcare

Transcript of Extending FHIR by Ewout Kramer