Transcript HL7 UK 2006: V3 Lite – Simplifying the Exchange of HL7 V3

V3 Lite – Simplifying the Exchange
of HL7 V3 Messages
Robert Worden
[email protected]
Summary
• Large message size and complexity is holding back
takeup of HL7 V3
• A V3 message definition can be restricted and reshaped
to make it smaller and simpler, without blurring
semantics
• The RMIM Reshaping Tool does this, keeping
mappings between full and reshaped messages
• XSLT transforms between full and reshaped messages
can made automatically and accurately
• This gives a simpler way to read and write V3 messages
from applications
• It can be used in several different scenarios
• It may be used to support a new ITS for V3
Complexity of HL7 V3
Why is HL7 V3 Complex and
Difficult to Use?
• HL7 technical committees are trying to address many
use cases, and to address them very thoroughly
• There are many intermediate ‘glue’ classes which add
little to the semantics
• CMETs are designed for many use cases; using them
adds complexity not needed for one use case
• Often a whole extra class has to be added, just to add
one attribute
• HL7 ways of building models (meta-model, methodology)
are complex and unlike vanilla UML
• RIM language is hard to understand, even for insiders
• Documentation is extensive and distributed
• HL7 tooling causes problems
XPath Counts – a Measure of
Message Complexity
• The number of distinct types of information that can be carried in a
message is roughly the number of distinct XPaths in the message
structure
• You need to cut off recursion (self-nesting) to keep this number finite
• For some V3 message definitions, the XPath count is very large
indeed:
• e.g. for a laboratory request message:
– 60,000 XPaths down to data type nodes
– More than 4 million XPaths down to leaf nodes
• A typical message instance may use only a few dozen of these
XPaths; finding them is hard
• V2 node counts are much smaller (and V2 is widely used…)
Tree depth and branching does it.
Try BD when D = 20
How to Implement V3 Messages
From the HL7 WIKI - V3 Implementation FAQ:
If you are working with XSLT you need to define an intermediate
XML format for your data.
This can be in "close to HL7" form or in "close to native" form.
It's normally sensible to quickly export your data in a near-native format,
and then encapsulate just the HL7 specifics in the XSLT.
V3
XSLT
XSLT
Intermediate
Intermediate
Application
1
App 1
Native
API
App 2
Native
API
Application
2
Problems With This Approach
• You have really just split the problem up into
pieces - not reduced it
• Transformations are needed in both directions
• 8 different transformations are needed for a
round trip:
[App 1 => App 2 => App 1]
• XSLT is not easy to write and test on this scale
• Will all 8 transformations be accurate?
HL7 V3 is like the National Grid; there is an
Impedance Mismatch with Everyday
Devices
Implementer
Domain 2
1,000 Volts?
110 Volts
V3 = 132,000 Volts
240 Volts
Implementer
Domain 1
How can we build accurate transformers
without prohibitive costs?
Restricted Message Profiles
• HL7 encourages realms (e.g. UK) and
implementors to constrain standard message
definitions into more restricted Profiles before
implementation
• Constrain means: reduce optionality and
cardinality ranges; constrain data types; …
• A message instance of the constrained definition
is an instance of the full definition
• The message skeleton remains more or less the
same size (e.g. depth); there is less flesh on it
Restricting and Reshaping
Message Definitions
• Restricting an RMIM means: restricting the cardinalities
of attributes and associations (above and within data
types) removing unused attributes and associations,
fixing values of attributes
• Reshaping an RMIM means: collapsing associations
which are 0..1 or 1..1; renaming classes, associations
and attributes, removing fixed attributes.
• In this way, the reshaped object model (and its XML
serialisation) can be made much simpler and more like a
DAM (domain analysis model)
• These operations preserve semantic equivalence
between the original and the reshaped model
• An instance of one can be transformed automatically to
be an instance of the other
Overview of RMIM Re-shaping
MIF
XSD
MIF
(reshaped)
XSD
RMIM
RMIM’
RMIM’’
Target
DAM
Reshaped RMIM
RMIM
Mappings
XML
Translation
XML
Instances
XMI
RMIM Reshaper Tool:
Screenshot/demo
Outputs of the Reshaping Tool (and
associated tools)
• Tables of mappings between RMIM and
reshaped class model
• MIF for reshaped class model
• XMI for reshaped class model
• XML Schema for reshaped XML messages
• Example message instances - for both full V3
XML ITS and reshaped XML
• XSLT transformations between full V3 XML and
reshaped XML (both directions)
Simpler Reshaped Class Model
cd ClinicalStatement
ClinicalStatementChoice
CHOICE
+ consent: Consent
+ observation: Observation
+ organizer: Organizer
+ procedure: Procedure
+ statementRelationship: StatementRelationship
+ substanceAdministration: SubstanceAdministration
+ supply: Supply
1..*
Supply
-
product: ManufacturedProduct
quantity: PQ
repeatNumber: IVL<INT>
0..*
StatementRelationship
Organizer
ACT
- specimen: Specimen
Observ ation
ACT
+ referenceRange: ReferenceValue
+ value: Any
PARTICIPANT
+ specimen: Specimen
Consent
ClinicalStatement
ACT
+ from: ActLink
+ to: ActLink
PARTICIPANT
+ author: AuthorStatement
+ performer: PerformerStatement
+ subject: SubjectRole
ACT
+ availabilityTime: TS
+ classCode: string
+ code: CV CNE
+ effectiveTime: TS
+ ID: II
+ moodCode: string
+ statusCode: CS
ACTRELATIONSHIP
+ contextdConductionInd: BL = true
+ inversionInd: BL = false
+ negationInd: BL
+ separateableInd: BL = true
+ sequenceNumber: INT
+ templateId: string
+ typeCode: string
Procedure
ACT
+ activityTime: TS
+ product: SpecimenRole
SubstanceAdministration
ACT
+ consumable: ManufacturedProduct
+ doseQuantity: IVL <PQ>
+ rateQuantity: IVL<PQ>
RELATEDACT
+ sourceOf: ActLink
+ supportingInfo: SupportingInformation
This example is cribbed from a paper by Ken Lunn,
(it is not output from the reshaping tool) and is purely illustrative.
The main point is that the number of classes and attributes is much fewer
than in an RMIM, and they have direct domain meanings.
Exemplar Message - Reshaped
<newPerson TelNumber="020 7711 435678" gender="1" dateOfBirth="28/11/1944" maritalStat="single">
<asEmployee>
<EmployerContactName familyName="Bellamy" givenName="James" namePrefix="Mr"/>
</asEmployee>
<guardian familyName="Summers" givenName="Adele" namePrefix="Mrs">
<addr countyName="Cambs" cityName="Cambridge" streetAddress="10 Garden Walk"/>
</guardian>
<birthPlace countyName="Lancs" cityName="Lytham" streetAddress="5 Ansdell Road"/>
<language code="EN" langName="English"/>
<name familyName="Prufrock" givenName="Alfred" namePrefix="Mr"/>
<address countyName="Cambs" cityName="Ely" streetAddress="5 Cathedral Walk"/>
</newPerson>
• This is a Patient Admin ‘New Patient’ message, restricted and
reshaped
• The exemplar was output from the reshaping tool
• Maximum depth of nesting is about 3
• Message size is 667 bytes
Exemplar Message – Full V3
<IdentifiedPerson classCode="IDENT">
<identifiedPerson classCode="PSN" determinerCode="INSTANCE">
<asEmployee classCode="EMP">
<employerOrganization classCode="ORG" determinerCode="INSTANCE">
<contactParty classCode="CON">
<contactPerson classCode="PSN" determinerCode="INSTANCE">
<name>
<family representation="TXT" mediaType="text/plain" partType="FAM">Bellamy</family>
<given representation="TXT" mediaType="text/plain" partType="GIV">James</given>
<prefix representation="TXT" mediaType="text/plain" partType="PFX">Mr</prefix>
</name>
</contactPerson>
</contactParty>
</employerOrganization>
</asEmployee>
<guardian classCode="GUARD">
<guardianPerson classCode="PSN" determinerCode="INSTANCE">
<name>
<family representation="TXT" mediaType="text/plain" partType="FAM">Summers</family>
<given representation="TXT" mediaType="text/plain" partType="GIV">Adele</given>
<prefix representation="TXT" mediaType="text/plain" partType="PFX">Mrs</prefix>
</name>
</guardianPerson>
……
•
•
•
•
Output from the reshaping tool, using the same instance data as before
Maximum depth of nesting is about 8
This is only part of the message
Full message size is 2431 bytes (4 times bigger than reshaped)
XSLT Translation and Round-Trips
• XSLT to translate from reshaped to V3, and back again,
is generated automatically from the mappings
• Generated XSLT files are large and boring
• The XSLT is not optimised yet, but is not stupid either
• It does round trips (reshaped – V3 – reshaped) with
100% accuracy
• Fixed attribute values are put into the V3 (or not if you
choose)
• XSLT is suitable, because there are no vocabulary
lookups (values are the same for V3 and reshaped
instances)
• Performance will be an issue for some high-volume
applications; we will start optimising then.
Comparative Query Tool
• Can query a V3 message instance and a
reshaped message instance, side by side in
terms of the reshaped class model
• Highlights differences in semantic content, in
colour
• A good way to check V3 messages for the
content that matters
• A good test of the accuracy of translations
• In the example that follows, I have introduced a
deliberate mistake (reshaped and V3 messages
are not quite equivalent)
Comparative Query –
Screenshot/Demo
Java API Using Reshaped Class
Model
• Can build Java applications in terms of the
reshaped (simpler, domain-like) class model
• The tools can generate skeleton Java classes
for the reshaped class model
• Can read V3 messages into these applications,
translating them automatically into the reshaped
class model via the mappings
• Applications are insulated from changes in V3
• This is like JavaSIG but uses the simpler class
model
What This Means for Implementors
• You need a MIF definition of the RMIM to start with
• You can then restrict and reshape it quite quickly with
the reshaping tool
• Illegal reshaping moves are forbidden by the tool
• XMI, XSD and XSLT are generated automatically
• The reshaped model becomes your intermediate XML
• You can then map your applications onto the (much
simpler) reshaped model, and read or write fully
conformant V3 into those apps.
• This saves a lot of effort
• It will increase the accuracy of your implementations
• It is fully V3-conformant, now
Usage Scenario – Fully V3
Conformant
V3
XSLT 1
XSLT 2
Intermediate
Intermediate
Application
1
App 1
Native
API
App 2
Native
API
Application
2
• Using reshaping, XSLT1 and XSLT 2 are generated automatically
and accurately
• Supplier 1 and supplier 2 can choose independently how to
implement (e.g. whether to use reshaping, how to reshape)
Usage Scenario – Smaller
Messages over the Wire
V3
XSLT 1
XSLT 2
Intermediate
Intermediate
Application
1
App 1
Native
API
App 2
Native
API
Application
2
• Reshaped message instances are typically 3-4 times smaller
• Supplier 1 and supplier 2 can still choose independently how to
implement (e.g. whether to use reshaping, how to reshape)
• Is that V3-conformant?
Usage Scenario – HL7.org defines
reshaped messages (New ITS)
V3 (old ITS)
XSLT 2
XSLT 1
V3 (New ITS)
Application
1
New ITS
App 1
Native
API
App 2
Native
API
Application
2
• HL7 defines reshaped RMIM as new ITS
• HL7 publishes XSLT to transform between them
• Suppliers can use either new or old ITS over the wire; both are
conformant V3
• Each supplier can choose independently whether to implement the
new ITS or the old ITS
Usage Scenario – CfH defines
reshaped messages
V3
XSLT 1
XSLT 2
New ITS
Application
1
New ITS
App 1
Native
API
App 2
Native
API
Application
2
• CfH publishes full and reshaped RMIMs in the MIM
• CfH publishes XSLT to transform between them
• Suppliers can use either new or old ITS over the wire; both are
conformant V3
• Each supplier can choose independently whether to implement new
or old ITS
V2-V3 Mapping Tool
• Pre-dates the reshaping tool, and has a similar user
interface
• Read in a V2 definition and a V3 definition; then define
mappings between them
• Translations can be generated automatically from the
mappings
• If an application already has a V2 interface, you could
use V2 XML as an intermediate XML on the way to V3
• Some HL7 TCs and suppliers have made and are
making V2-V3 mappings
• Mappings are exchangeable in the tool format
Current Status
• NPfIT are now evaluating approaches to
message simplification and the new XML-UML
ITS, including use of the RMIM reshaping tool
• Example messages being tested: GP summary,
ETP, PDS, ….
• Results will be presented at the HL7 WGM in
San Diego in January
• The RMIM reshaper will soon be available from
the HL7 Homebase (tooling site)
What will be Open Source
•
•
•
•
•
RMIM Reshaping tool
V2-V3 Mapping tool
Java API for messages
Java class generator
Comparative Query Tool
What will be Licensed
• XSLT Generator
• Run-time translation engine
• Translation compiler
Questions
For full slides with notes, see the
conference site.
For further information, email
[email protected]