Transcript Implementing Web Services for Healthcare

Implementing Web Services for
Healthcare
Lessons & Pitfalls
- Marc de Graauw 1
NICTIZ & Dutch Healthcare
• Standardization authority for data
exchange in Dutch healthcare
• Short term goal: national exchange of
medication data operational in 2006
• 90.000 people are hospitalized yearly due
to wrong medication
• "The question is not whether the electronic
medical file will become obligatory, but
how" – Min. Hoogervorst
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NICTIZ & Dutch Healthcare
• Communication between:
– Healthcare Provider (GP, hospital etc.)
– Healthcare Information Broker (HIB)
• HIB provides:
– index of which parties have patient data
– no patient data itself
– messaging services
– aggregation services
• Health Level Seven version 3 (HL7v3)
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Healthcare
Information
Broker
Healthcare
Information
System
Messaging
Services
Healthcare
Information
System
Healthcare
Information
System
Healthcare
Information
System
Patient
Registry
Healthcare
Information
System
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Just enough HL7
• HL7 version 2 : currently used
• HL7v3:
– XML based
– Reference Information Model
• HL7v3 Message contains:
– medical payload
– Trigger Event Wrappers (Query Control etc.)
– Transmission Wrapper
• Example: QURX_EX990001NL-1.xml
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HL7v3 Layered Model
HTTP, SSL
SOAP / XML
HL7 Transmission Wrapper
HL7 Query Control Wrapper
HL7 Medical Data
TCP
lower protocol layers
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Transmission Wrapper
• Addressing information (Sender, Receiver)
• MessageId (unique id / message)
– duplicate detection is requirement
• Accept Acknowledgement Code
– request accept acknowledgement (Never / Always,
Error, Succes)
– is syntactical – not semantic – acceptance
• more...
• Contains other wrappers
• Transmission Wrapper intersects web services
stack
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Which standards?
• The basics were pretty clear:
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HL7v3
XML 1.0 & Namespaces
XML Schema
SOAP 1.1 (not a real standard!)
• In 2003 when work started:
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SOAP 1.2 not finished
WSDL 1.1 finished, 2.0 not
WS-stack not finished (Reliability, Security etc.)
ebXML Messaging (ebMS)
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SOAP in one slide
• Envelope, Headers, Body
<soap:Envelope ... namespaces ... >
<soap:Header mustUnderstand = ‘1’>
... headers ...
</soap:Header>
<soap:Body>
... payload ...
</soap:Body>
</soap:Envelope>
• HTTP Binding
POST / HTTP/1.1
bla bla...
SOAPAction: "urn:hl7-org:v3/QURX_AR990120NL“
<?xml version="1.0" encoding="utf-8"?>
<soap:Envelope ... namespaces ... >
• SOAP Encoding: legacy, forget it
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Which standards?(cont.)
• Security? No.
–
–
–
–
we use HTTPS
intermediaries (HIB) are trusted
this is secure
later: WS-Security, XML Signature, XML Encryption
• Addressing? No.
– HL7v3 provides own addressing scheme
• Description? Maybe.
– HL7v3 has own interaction modelling methodology
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Which standards?
• Reliability? Yes.
– transport over HTTP is not reliable
• The options?
– ebMS 2.0
• no IBM, Microsoft adoption
– WS-Reliability (Sun, Oracle et. al.)
• not finished
– WS-ReliableMessaging (IBM< Microsoft et. al.)
• not finished, (was?) proprietary
– HL7v3 Accept Acks
• Confused?
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Sender
Receiver
Message
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Sender
Receiver
Message
Copy of Message
Receipt Ack
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Sender
Receiver
Message
Receipt Ack
Copy of Message
Receipt Ack
Does duplicate detection
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Which standards? (cont.)
•
•
•
•
•
Basics were clear (XML, XSD, SOAP)
WSDL added (well standardized & used)
No need for discovery / repository specs
Future of some WS standards uncertain
Adopt as few standards as possible
– No lock-in to wrong (= losing) ‘standard’
– Facilitate later adoption
– SOAP Headers make transition easier
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Lessons & Pitfalls
• Lesson 1: Do not adopt standards too
soon!
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‘Real world’ complexity
• HL7v3 XML Schema <include> stacks of
10 – 15 schemas
• HL7v3 typing system (mapped onto XSD
datatypes)
• HL7v3 vocabulary
• Layered ‘wrapper’ approach
• SOAP (Transmission (Query (Medical
Data)))
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WSDL in one slide
• WSDL defines a web service
• Which schemas are used?
• Which messages are used & which
schemas are involved?
• Which operations are used & which
messages go in and which go out?
• How do operations assemble to make a
web service (PortType, Service)?
• Binding to SOAP and HTTP
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Medication Query Service
Query
Schema
Medication Query PortType
QueryResponse Operation
Binding
Query Message
Response Message
Other Operation
Response
Schema
Other PortType
Other PortType
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‘Real world’ complexity (cont.)
• WSDL is a:
– description of a web service
– generate WSDL from code?
– generate code from WSDL?
• WSDL code generation
– map XML to programming object
•
•
•
•
•
•
<birthdate>19610306</birthdate>
maps to: date
<name><first>Marc</first><last>de Graauw</last></name>
maps to: struct of string, string
<gender>M</gender>
maps to: char(1) or: enum(‘M’, ‘F’) or: GenderType
– map operations, HTTP Binding et cetera
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‘Real world’ complexity (cont.)
• WSDL code generation:
– reserved word clashes
– creates object for each XML construct
– 15 schemas -> Gargantuan objects!
– all of vocabulary.xsd
– all objects in one module
• Code generation: fine for
– float FahrenheitToCelsius(float)
– currency StockQuote(string)
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Lessons & Pitfalls
• Lesson 1: Do not adopt standards too
soon
• Lesson 2: Do not count on code
generation
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Dynamic response types
• WSDL: operation with defined message
types with defined Schemas
• HL7v3 has attributes where content codetermines response Schema
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Dynamic response
• HLv3 responseModalityCode = “R”
Some
HL7v3
Query
Schema
Some HL7v3 PortType
Some HL7v3 Query
Binding
Some HL7v3 Query
HL7v3 Query Response
HL7v3
Query
Response
Schema
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Dynamic response (cont.)
• HLv3 responseModalityCode = “B”
Some
HL7v3
Query
Schema
Some HL7v3 PortType
Some HL7v3 Query
Binding
Some HL7v3 Query
HL7v3 Response Batch
HL7v3
Batch
Response
Schema
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Dynamic response (cont.)
• More HL7v3 attributes (=XML elements)
– acceptAckCode
– responsePriority
– continuationQuantity
• content co-determines response Schema
• Solutions:
– multiple PortTypes = clutter, bad design
– <choice> in Schema = undescriptive, hard to
read
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Lessons & Pitfalls
• Lesson 1: Do not adopt standards too
soon
• Lesson 2: Do not count on code
generation
• Pitfall 1: Dynamic response types
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Generic vs. specific WSDL
• Specific WSDL:
HL7v3 Medication PortType
HL7v3 Medication
QueryResponse
Operation
HL7v3
Medication
Query
Schema
Binding HL7v3 Medication Query
HL7v3 Medication Response
HL7v3
Medication
Response
Schema
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Generic vs. specific WSDL
• Generic WSDL:
HL7v3
Message
Schema
HL7v3 Message PortType
HL7v3 Message
Operation
Binding
HL7v3 MessageOut
HL7v3 MessageIn
HL7v3
Message
Schema
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Generic vs. specific WSDL
• Generic WSDL uses generic Schemas
<xs:schema targetNamespace="urn:hl7-org:v3">
<xs:element name="hl7Message">
<xs:complexType>
<xs:sequence>
<xs:any/>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:schema>
• Possibly with Transmission Wrapper
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HL7 Medical Application
HL7v3
medical
content
HL7 Control Query Processing Application
HL7v3
CQ Wrapper
& payload
HL7 Transmission Wrapper Adapter
HL7v3
messages
HL7 web services Messaging Adapter
SOAP
messages
HTTP Client / Server
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Generic WSDL
• Pro:
– eases separation of layers
– no problems with dynamic response
– code generation is useful again
• Con:
– does not describe actual web service neatly
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Lessons & Pitfalls
• Lesson 1: Do not adopt standards too
soon
• Lesson 2: Do not count on code
generation
• Pitfall 1: Dynamic response types
• Lesson 3: Consider generic WSDL
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Reliability Issues
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We chose HL7v3 Accept Acks
unclarity in standards situation
2003/4: standards not finished
SOAP allows extension
but: commit / accept blur!
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Reliability Issues
• Delegated to HTTP 200 OK
HL7v3 Medication PortType
HL7v3 Medication
QueryResponse
Operation
HL7v3
Medication
Query
Schema
Binding HL7v3 Medication Query
HL7v3 Medication Response
HL7v3
Medication
Response
Schema
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Reliability Issues
• Using Accept Acknowledgements
HL7v3 Medication PortType
HL7v3 Medication
Query
Operation
HL7v3 Medication
Response
Operation
Binding HL7v3 Medication Query
HL7v3 Accept Ack
Binding
HL7v3 Med. Response
HL7v3 Accept Ack
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Reliability Issues
• Delegate to HTTP 200 OK
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–
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only for idempotent messages
synchronous
one side only needs SOAP client
single HTTP request – response pair
• Accept Acks
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–
–
works for all messages
asynchronous
both sides need SOAP server
two HTTP request – response pairs
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Lessons & Pitfalls
• Lesson 1: Do not adopt standards too
soon
• Lesson 2: Do not count on code
generation
• Pitfall 1: Dynamic response types
• Lesson 3: Consider generic WSDL
• Lesson 4: Carefully design Bindings
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Wire signatures
• We chose to follow WS-I Basic Profile
– sensible set of guidelines
– not an additional standard
– refinement of SOAP 1.1 / WSDL 1.0
• R2710: operations MUST result in wire
signatures that are different
• R2710: wire signature = name of the child
element of the soap:Body
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Wire signatures
• Continuation: continuationQuantity > 0
• Cancel: continuationQuantity = 0
HL7v3 Medication PortType
HL7v3 Medication
QueryContinuation
Operation
HL7v3 Medication
QueryCancel
Operation
Binding HL7v3 QueryContinuation
HL7v3 Med. Response
Binding
HL7v3 QueryCancel
HL7v3 Accept Ack
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Lessons & Pitfalls
• Lesson 1: Do not adopt standards too
soon
• Lesson 2: Do not count on code
generation
• Pitfall: Dynamic response types
• Lesson 3: Consider generic WSDL
• Lesson 4: Carefully design Bindings
• Pitfall: R2710 & wire signatures
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The ebMS story
• ebMS
– used in NHS (British Healthcare)
– Dutch Criminal Justice Chain
– Dutch Social Security Chain (BKWI)
– NICTIZ reconsidered
– did not adopt ebMS now: stability of specs
• Lesson 1: Do not adopt standards too
soon
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Marc de Graauw
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Independent Consultant
... and I like it!
not available till sometime in summer
www.marcdegraauw.com
[email protected]
Feedback welcome!
• QUESTIONS .... ???
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