Validation in net and java (ewout james)

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Amsterdam, 15-17 November | @fhir_furore | #fhirdevdays17 | www.fhirdevdays.com
Validation in .NET and Java
Ewout Kramer, Furore Health Informatics and James Agnew, University Health Network

Who am I?
 Name: Ewout Kramer
 Company: Furore Health Informatics
 Background:
 Computer Science (operating systems)
 In Health IT since 1999
 FHIR Core team
 Lead dev on the .NET API
 e.kramer@furore.com, @ewoutkramer
 http://thefhirplace.com2

Who am I?
 Name: James Agnew
 Company: UHN / Smile CDR
 Background:
 Lead dev on the Java HAPI library
 jamesagnew@gmail.com, @jamesagnew
3

Validation inputs
 Instance data (resource)
 Definition of what data should look like (StructureDefinitions)
 Terminology services (ValueSet)
 Execution of FhirPath constraints
 Some way to combine it all, validate and return the outcomes
4

VALIDATION IN .NET
5

Structure of packages
6
Hl7.Fhir.Support
(Net4, Net4.5, Net1.0, Net1.3)
• Utility methods
• ElementModel
Hl7.FhirPath
(Net4, Net4.5, Net1.0)
• FhirPath compilation
• FhirPath evaluation
Hl7.Fhir.Core
(Net4.5, Net1.1, Net1.3)
• Model classes
• Serialization
• Http client
Hl7.Fhir.Specification
(Net4.5, Net1.3)
• Access to definitions
• Terminology services
• Validation

Instance data:
IElementNavigator
7

Specification data
 All the definitions of the core resources, types, search
parameters, operations, etc. are available through the
Hl7.Specification.[STU3/DSTU2] package on NuGet
 The package contains a zip (specification.zip) with meta data
produced by the FHIR publication process
 profiles-resources.xml, profiles-types.xml, extension-definitions.xml
 search-parameters.xml
 v2-tables.xml, v3-codesystems.xml, valuesets.xml
 xsd schemas, schematrons, others....

Definitions: IResourceResolver
 Concrete implementations in API:
 DirectorySource, ZipSource
 WebSource
 CachedResolver (wraps another resolver)
 MultiResolver (tries a list of resolvers)9

Terminology:
ITerminologyService
 Current implementations:
 LocalTerminologyService
Does an in-memory expand & lookup
 ExternalTerminologyService
Uses the FhirClient calls to validate a code (possibly even
sending your valueset across!)
 FallbackTerminologyService
First tries LocalTerminologyService, if that fails (too
complex!), invoke an external service
 Note: returns OperationOutcome
10

The Big Picture
FHIR Data
<Patient>
</Patient>
IElementNavigator FHIR Definitions
StructureDefinition
OperationDefinition
ValueSet
IResource
Resolver
FindStructure
Definition()
ValueSetExpander
LocalTerminology
Service
ITerminologyService
Validator
FluentPathCompiler
FHIR Poco
OperationOutcome
(with IssueComponents)
ExternalTerminology
Service

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
12

13

Caveats
 Validator is still being improved
 Support most features already, except for slicing – only
discriminator-less slicing is supported
 Other improvements: e.g. loop-detection
14

Playing with the validator
 Windows executable:
 https://github.com/ewoutkramer/Furore.Fhir.ValidationDemo/releases
 Directly calling the Validator in code
 Using “Validate” on Simplifier.net
15

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)
16

QUESTIONS?

VALIDATION IN HAPI FHIR
Suggestions for a pleasurable afternoon

When and how to Validate
There is no right answer to this question!
 Validate strictly during development but be loose in
production? Always be strict?
 Validate some resource types but not others?
 Validate on the way in but not the way out?
 Structural vs semantic validation? (there is a performance
cost!)

Validation in HAPI FHIR
Parser Error Handler
(structural validation only)
● Parser can be configured
with an “Error Handler”
which logs or fails on error
● Only catches structural
issues
Validator
(semantic validation)
● Applies a complete set of
rules to a resource instance
● Currently far more powerful

Parser Error Handler
 Callback mechanism during parsing
 Very fast!
 Catches structural problems:
 Invalid elements
 Invalid cardinalities
 JSON data type mismatches
21

Parser Validator
String input = "{"resourceType":"Patient","isnice":true}";
FhirContext ctx = FhirContext.forDstu3();
IParser parser = ctx.newJsonParser();
parser.setParserErrorHandler(new LenientErrorHandler(true));
parser.parseResource(input);
22

Parser Validator
parser.setParserErrorHandler(new LenientErrorHandler(true));
23
[main] WARN
ca.uhn.fhir.parser.LenientErrorHandler -
Unknown element 'isnice' found while
parsing

Parser Validator
parser.setParserErrorHandler(new StrictErrorHandler());
24

Parser Validator
parser.setParserErrorHandler(new StrictErrorHandler());
25
ca.uhn.fhir.parser.DataFormatException:
Unknown element 'isnice' found during parse

Profile Validation
 Applies semantic validation based on “Profiles”
 Slower than parser error handler!
 Validates various things:
 All the same structural validation as parser error handler
 Terminology bindings
 Invariants
 Constraints and extensions
26

Validator
● HAPI’s validator uses modules and collects the results from
any that are enabled
● Create your own if you want!

Schema/Schematron Validator
 FHIR provides schemas + schematrons for validating
conformance to basic resource requirements:
 Cardinality
 Optionality
 Required bindings
 Datatype rules
 The Schema + Schematron modules are the defaults if
nothing else is selected

Schema/Schematron Validator (2)
Dependencies:
● hapi-fhir-validation-resources-dstu3-2.5.jar
● phloc-schematron-2.7.0.jar
Inputs (pick one):
● Resource Java model object
● Raw JSON Resource
● Raw XML Resource

Using the Schema Validator
public class Example20_ValidateResource {
public static void main(String[] args) {
// Create an incomplete encounter (status is required)
Encounter enc = new Encounter();
enc.addIdentifier().setSystem("http://acme.org/encNums").setValue("12345");
// Create a new validator
FhirValidator validator = ctx.newValidator();
// Did we succeed?
ValidationResult result = validator.validateWithResult(enc);
System.out.println("Success: " + result.isSuccessful());
// What was the result
OperationOutcome outcome = (OperationOutcome) result.toOperationOutcome();
IParser parser = ctx.newXmlParser().setPrettyPrint(true);
System.out.println(parser.encodeResourceToString(outcome));
}
}

Using the Schema Validator
public class Example20_ValidateResource {
// Did we succeed?
ValidationResult result = validator.validateWithResult(enc);
}
}
<OperationOutcome xmlns="http://hl7.org/fhir">
<issue>
<severity value="error"/>
<code value="processing"/>
<diagnostics value="cvc-complex-type.2.4.b: The content of
element 'Encounter' is not complete. One of
'{"http://hl7.org/fhir":identifier,
"http://hl7.org/fhir":status}' is expected."/>
<location value="Line[1] Col[140]"/>
</issue>
</OperationOutcome>
false

Schema Validation with String Input
Strings are also valid input (JSON is converted to XML!)public class Example21_ValidateResourceString {
String input = "<Encounter xmlns="http://hl7.org/fhir"></Encounter>";
// Did we succeed?
ValidationResult result = validator.validateWithResult(input);
}

Profile Validation
 In FHIR, a “Profile” is a collection of special resources:
 StructureDefinition
 ValueSet
 CodeSystem
 A resource can declare conformance to a profile in its
metadata
 A server can require conformance to a profile

Profile Validator
● FhirInstanceValidator module requires an instance of
IValidationSupport
● Several implementations are supplied with HAPI FHIR
● You can also create your own

Validation Support
Use built-in FHIR definitions and terminology
Load your own definitions and terminology
Chain multiple providers together

Questionnaires are Validated
● FhirInstanceValidator will also validate
QuestionnaireResponse compliance to
Questionnaire

Using the Profile Validator
public class Example22_ValidateResourceInstanceValidator {
FhirValidator validator = FhirContext.forDstu3().newValidator();
// Cache this object! Supplies structure definitions
DefaultProfileValidationSupport support = new DefaultProfileValidationSupport();
// Create the validator
FhirInstanceValidator module = new FhirInstanceValidator(support);
validator.registerValidatorModule(module);
// Did we succeed?
IParser parser = FhirContext.forDstu3().newXmlParser().setPrettyPrint(true);
System.out.println(parser.encodeResourceToString(validator.validateWithResult(enc).toOperationOutcome()));
}
}

Using the Profile Validator
public class Example22_ValidateResourceInstanceValidator {
FhirValidator validator = FhirContext.forDstu3().newValidator();
// Cache this object! Supplies structure definitions
DefaultProfileValidationSupport support = new DefaultProfileValidationSupport();
// Create the validator
FhirInstanceValidator module = new FhirInstanceValidator(support);
validator.registerValidatorModule(module);
// Did we succeed?
IParser parser = FhirContext.forDstu3().newXmlParser().setPrettyPrint(true);
System.out.println(parser.encodeResourceToString(validator.validateWithResult(enc).toOperationOutcome()));
}
}
<OperationOutcome xmlns="http://hl7.org/fhir">
<issue>
<severity value="error"/>
<code value="processing"/>
<diagnostics value="Profile
http://hl7.org/fhir/StructureDefinition/Encounter, Element
'Encounter.status': minimum required = 1, but only found 0"/>
<location value="Encounter"/>
</issue>
</OperationOutcome>

39

HANDS-ON TRACK
Suggestions for a pleasurable afternoon

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…)
41

Validation in net and java (ewout james)

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