Health Level Seven Experience Report

1
Health Level SevenExperience Report

• Paul V. Bironpaul.v.biron_at_kp.org
• Kaiser Permanente

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

• HL7 Healthcare messaging and documents
• Things We Like
• Interoperability Problems
• Expressiveness Problems

3
Things We Like

• XML Syntax
• easier to generate and reuse
• Separation of Elements and Types
• the fuel that drives binding tools
• cant wait for XPath 2.0s type-aware matching
  (independent of element/attribute names)
• Type derivation
• extension and restriction
• almost identical to our abstract UML-based model

4
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)

5
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 dont use it much

6
Expressiveness Problems

• Extend only at end

ltpersongt ltname/gt lt!-- Entity --gt
ltbirthTime/gt lt!-- Living Subject --gt
ltdesceasedTime/gtlt!-- Living Subject --gt
ltaddress/gt ltrace/gt ltplayergt lt!-- Entity
--gt ... lt/playergt ltscopergt lt!--
Entity --gt ... lt/scopergt lt/persongt
ltpersongt ltname/gt lt!-- Entity --gt
ltplayergt lt!-- Entity --gt ...
lt/playergt ltscopergt lt!-- Entity --gt
... lt/scopergt ltbirthTime/gt lt!--Living
Subject--gt ltdesceasedTime/gtlt!--Living
Subject--gt ltaddress/gt lt!-- Person --gt
ltrace/gt lt!-- Person --gtlt/persongt
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Expressiveness Problems

• Lack Of Co-Occurance Constraints
• Almost every type we define as co-occurance
  constraints
• as a result, weve 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

8
Expressiveness Problems

• Wildcards deficiencies
• need ltxsany typefoo/gt
• similar to substitution groups, but doesnt
  require global elements
• interaction with UPA
• weak wildcards would be a big win
• Component Identity Vagueness
• cant derive by restriction from a type which
  uses anonymous types ?
• hence, weve had to name types we would not
  otherwise

9
Expressiveness Problems

• Limitations On All Groups

ltxscomplexType name'Person'gt ltxssequencegt
ltxsallgt ltxselement name'name'/gt
ltxselement name'birthTime'/gt
ltxselement name'desceasedTime'/gt
ltxselement name'address'/gt
ltxselement name'race'/gt lt/xsallgt
ltxsallgt ltxselement name'scopes'/gt
ltxselement name'plays'/gt lt/xsallgt
lt/xssequencegt lt/xscomplexTypegt
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lt?Questions?gt

• ... and answers