Advanced .NET API (Ewout)

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Advanced.NET API

Ewout KramerFHIR Developer DaysNovember 17, 2016


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Who am I?

Name: Ewout Kramer Company: Furore Background:

Computer Science (operating systems) In Health IT since 1999 FHIR Core team Lead dev on the .NET API

[email protected], @ewoutkramer http://thefhirplace.com

mailto:[email protected]


BEYOND THE POCO

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Why?

No need to parse whole POCO’s in memory Generic clients/servers not needing pre-

compiled model classes Tools that can parse (partly) invalid FHIR

data Accessing DSTU2 and STU3 data


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“Logical” structure of FHIR data


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IElementNavigator

Represents a position in a tree of FHIR data Has all the aspects of a node (from last slide) Path: Patient.name[1].family[0]


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INavigator<T>

GetChildrenByName(this IElementNavigator navigator, string name)

IEnumerable<object> Values(this IElementNavigator navigator)


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Caveat

We are showing you work in progress Interfaces may change Will be implemented for DSTU2 and STU3 Currently prackaged as part of the

FluentPath .NET Core library (HL7.FluentPath)

Use the latest 0.4.x (alpha) releases Only available implementation is the PocoNavigator


GETTING TO METADATA


Conformance Resources

Provide “metadata” about Model Definitions (StructureDefinition) Operations (OperationDefinition) Search parameters (SearchParameter) List of codes (ValueSet)

Identified by a “canonical url” that SHOULD resolve, e.g. “http://hl7.org/fhir/StructureDefinition/Patient”


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Resolution

Directly using a FHIR REST call to the url More likely:

As part of a “snapshot”/zip of files delivered with your app

Compiled into your app In a database


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IResourceResolver

Concrete implementations in API: DirectorySource, ZipSource WebSource CachedResolver (wraps another resolver) MultiResolver (tries a list of resolvers)


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Combine at will

MyDbResolver ZipSource WebResolver

MultiResolver

CachedResolverMultiResolver


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Practicalities

Packaged in Hl7.Fhir.Specification assembly Namespace Hl7.Fhir.Specification.Source Includes useful extension methods like:

FindStructureDefinition(this IResourceResolver resolver, string uri, bool requireSnapshot = false)

FindStructureDefinitionForCoreType(this IResourceResolver resolver, FHIRDefinedType type)

FindExtensionDefinition(this IResourceResolver resolver, string uri, bool requireSnapshot = false)

Data for base spec is in “specification.zip”, easy to get to using ZipSource.CreateValidationSource()


TERMINOLOGY


FHIR Resources

CodingSystem resource (STU3) A dictionary of concepts (possibly huge!)

ValueSet (DSTU2, STU3) A (use-case specific) selection of concepts from

1..* CodingSystems May be directly enumerated (‘extensional’) May be composed using filters (‘intensional’)

“all the LOINC codes in LOINC Part Concept Cholesterol | Bld-Ser-Plas (LP43571-6), except for 5932-9 Cholesterol [Presence] in Blood by Test strip”

May be composed from other ValueSets


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Main functionality

Expand an intensional ValueSet Determine whether some code is member of

a ValueSet Do a code-lookup

Find details like alternative designation

Could be done “in-memory” (i.e. using an expanded ValueSet)

By calling the FHIR terminology operations


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In-memory

Expand using the ValueSetExpander class in Hl7.Fhir.Specification.Terminology

Set limits on expansion size Uses IResourceResolver to locate

ValueSets Current limitations:

No filters No imports of whole CodeSystems


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Working with the expansion Useful extension methods on ValueSet

HasExpansion() ExpansionSize() FindInExpansion(String code, string system) bool CodeInExpansion(String code, string system)

Note: no automatic expansion, use ValueSetExpander


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Terminology operations

https://www.hl7.org/FHIR/valueset-operations.html

$expand, $lookup, $validate-code

class FhirClient ExpandValueSet() ConceptLookup() ValidateCode()




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ITerminologyService

Currently available: LocalTerminologyServer Does an in-memory expand & lookup

Planned: try cache - then the LocalTerminologyServer - then the operations on a “real” terminology server.

Note: returns OperationOutcome


FHIRPATH SUPPORT

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FhirPath in .NET

First, the name FhirPath -> FluentPath -> FhirPath

Available as a .NET Core library Hl7.FluentPath on NuGet (0.4.x)

Is built on top of IElementNavigator – so it could work on *any* object model


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Compiling FhirPath

Advantage: Compile once, run many (fast) class FluentPathCompiler public CompiledExpression Compile(string expression)

CompiledExpression is a native Lambda that will run the statement against an IElementNavigator

You can also compile to an Expression tree (for debug/display purposes)


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Using CompiledExpression First, compile the statement

var ce = compiler.Compile(“Patient.name”);

Then: var result = ce(…) result is a set of IElementNavigators

Or: object s = ce.Scalar(…); bool p = ce.Predicate(…); bool b = ce.IsBoolean(true, …);


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Convenience methods

Comparable methods exist on IElementNavigator so you can directly query a source of data

Example: IElementNavigator nav = new PocoNavigator(myPatient); object cnt = nav.Scalar(“Patient.name.count()”); Compiles & caches last 500 expressions for

you


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On POCO’s directly…

The Hl7.Fhir.Core assembly has extension methods in Hl7.Fhir.FluentPath for working directly on FHIR POCO’s

Patient p = …;object cnt = p.Scalar(“Patient.name.count()”);


VALIDATION


The Big PictureFHIR Data

<Patient></Patient>

IElementNavigator FHIR Definitions

StructureDefinitionOperationDefinitionValueSet

IResource Resolver

FindStructure Definition()

ValueSetExpander

LocalTerminology Server

ITerminologyService

Validator

FluentPathCompiler

FHIR Poco

OperationOutcome(with IssueComponents)


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Practicalities

class Validator in Hl7.Fhir.Validation namespace (Hl7.Fhir.Specification assembly)

Configure: new Validator(settings) Resolver, terminology service to use

Validate: call one of the overloads: Validate(IElementNavigator) Validate(Base) Validate(XmlReader)

Result is an OperationOutcome


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Caveats

Validator is still being developed as we speak

Support most features already, except for slicing – only discriminator-less slicing is supported

Other improvements: e.g. loop-detection

Almost daily updates with more functionality


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OperationOutcome- on steroids Lots of helper methods Properties:

Success (!information,!warning) Fatals, Errors, Warnings properties

Extension methods (in Hl7.Fhir.Support) ErrorsAt(string path) Where(severity, type, …) Set/GetHierachyLevel() Include(outcome), Add(outcome)


QUESTIONS?

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HANDS-ON TRACKSuggestions for a pleasurable afternoon


IResourceResolver

Try to use the ZipSource with the specification.zip to get some core resource definitions

Write your own IResourceResolver that resolves from a .NET compiled-in resource (not a FHIR resource ;-)


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ITerminologyService

Use your new IResourceResolver to resolve a ValueSet & expand it.

Use ValueSet’s FindInExpansion to verify whether you succeeded

Look at the C# implementation of LocalTerminologyService. Could you make one that calls the FhirClient.ValidateCode() instead?


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Play with the validator Check out https://

github.com/ewoutkramer/Furore.Fhir.ValidationDemo & compile

Try to incorporate your resolver and terminology service (if any)

Try running the examples at https://github.com/ewoutkramer/fhir-net-api/tree/develop/src/Hl7.Fhir.Specification.Tests/TestData/validation

Alter the examples so they trigger your code (change a binding…)

https://github.com/ewoutkramer/Furore.Fhir.ValidationDemo

https://github.com/ewoutkramer/Furore.Fhir.ValidationDemo

https://github.com/ewoutkramer/fhir-net-api/tree/develop/src/Hl7.Fhir.Specification.Tests/TestData/validation




HIDDEN GEMS


ResourceIdentity

class ResoureIdentity : Uri Builds FHIR RESTful Uri’s Factory methods Build():

.Build(“Patient”, “4E75”, vid: “4”) “/Patient/4E75/_history/4”

StructureDefinition URLs for core types .Core(FHIRDefinedType.HumanName)

“http://hl7.org/fhir/StructureDefinition/HumanName”


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ResourceIdentity (2)

Even more useful: parsing RESTful Urls var ep = “http://server.org/fhir/Patient/4”

var u = new ResourceIdentity(ep);

u.ResourceType “Patient”

u.Id “4”


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Extension Manipulations


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TransactionBuilder


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SnapshotGenerator

Advanced .NET API (Ewout)

Healthcare