Health Level SevenExperience Report

Paul V. Bironpaul.v.biron@kp.org

Kaiser Permanente

W3C XML Schema User Experience Workshop, Jun 21-22, 2005

2HL7 Schema Experience Report W3C XML Schema User Experience Workshop, Jun 21-22, 2005

Intro• HL7: Healthcare messaging and documents

• Things We Like

• Interoperability Problems

• Expressiveness Problems

3HL7 Schema Experience Report W3C XML Schema User Experience Workshop, Jun 21-22, 2005

Things We Like• XML Syntax

– easier to generate and reuse

• Separation of Elements and Types– the fuel that drives binding tools– can’t wait for XPath 2.0’s type-aware matching

(independent of element/attribute names)

• Type derivation– extension and restriction– almost identical to our abstract UML-based model

4HL7 Schema Experience Report W3C XML Schema User Experience Workshop, Jun 21-22, 2005

Interoperabiltiy Problems• Complicated Writing Style

– makes it very difficult for the “average” person to understand the spec

– feel this is largely responsible for the disagreements that various processors have about the spec

• Features Incorrectly (or Not At All) Implenented– chameleon include (validators, editors) – mixed content (data binding) – failure to signal UPA violations (editors) – regular expression/pattern matching (validators) – abstract types (validators) – element/type name to programming language identifier

mapping problems (data binding)

5HL7 Schema Experience Report W3C XML Schema User Experience Workshop, Jun 21-22, 2005

Expressiveness Problems• Extend Only At End

– complex types generated from UML classes– extension is used for one class specializing another– we serialize UML attributes before UML associations– extend only at end made out instances “ugly”, hence we

don’t use it much

6HL7 Schema Experience Report W3C XML Schema User Experience Workshop, Jun 21-22, 2005

Expressiveness Problems• Extend only at end

<person> <name/> <!-- Entity --> <birthTime/> <!-- Living Subject --> <desceasedTime/><!-- Living Subject --> <address/> <race/> <player> <!-- Entity --> ... </player> <scoper> <!-- Entity --> ... </scoper> </person>

<person> <name/> <!-- Entity --> <player> <!-- Entity --> ... </player> <scoper> <!-- Entity --> ... </scoper> <birthTime/> <!--Living Subject-->

<desceasedTime/><!--Living Subject--> <address/> <!-- Person --> <race/> <!-- Person --></person>

7HL7 Schema Experience Report W3C XML Schema User Experience Workshop, Jun 21-22, 2005

Expressiveness Problems

• Lack Of Co-Occurance Constraints– Almost every type we define as co-occurance

constraints• as a result, we’ve had to make everything optional

– occurance-based vs. value-based co-occurance– HL7 would be satisfied if XML Schema had occurance-

based constraints, although we have a few use cases for value-based

8HL7 Schema Experience Report W3C XML Schema User Experience Workshop, Jun 21-22, 2005

Expressiveness Problems• Wildcards deficiencies

– need <xs:any type=‘foo’/>• similar to substitution groups, but doesn’t require global

elements– interaction with UPA

• “weak wildcards” would be a big win

• Component Identity Vagueness– can’t derive by restriction from a type which uses

anonymous types – hence, we’ve had to name types we would not

otherwise

9HL7 Schema Experience Report W3C XML Schema User Experience Workshop, Jun 21-22, 2005

Expressiveness Problems• Limitations On All Groups

<xs:complexType name='Person'> <xs:sequence> <xs:all> <xs:element name='name'/> <xs:element name='birthTime'/> <xs:element name='desceasedTime'/> <xs:element name='address'/> <xs:element name='race'/> </xs:all> <xs:all> <xs:element name='scopes'/> <xs:element name='plays'/> </xs:all> </xs:sequence> </xs:complexType>

... and answers

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