new its investigation nhs cfh research report grahame grieve, laura sato, charlie mccay
TRANSCRIPT
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New ITS Investigation
NHS CfH Research Report
Grahame Grieve, Laura Sato, Charlie McCay
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Agenda
• Status• Findings• Issues• What is the use of XML Element Names• Datatype proposals• Methodology proposals• UML ITS proposals• Examples
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Status
This presentation has been prepared for HL7UK to summarise development in the NHS CFH New ITS investigation.
We will seek during the consultation day to produce a variation on this presentation that can be taken to HL7.org with the support of HL7UK
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Findings
• Domain Analysis Models
• Implementation Experience
• Removal of Fixed Values
• Interesting background– H7v3 as storage format– CEN / HL7 harmonisation
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Domain Analysis Models
• Business names useful
• Do not capture “non-functional” requirements (eg those that impact SLAs)
• Mapping exercise useful, but not the best way to shape models for implementation.
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Implementation Concerns
• V3 judged on implementation experience, examples and schemas
• Few do detailed background work that javaSIG has done
• Most start their implementations using the schemas, but end up finding them much less useful than expected
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Key Implementation Problems
• Node count and deep nesting, with each XML element requiring processing by developer and application
• Schema do not support tools or code reuse• Requirements to instance mapping not clear• Datatype property constraints hard• Model Reuse (20 similar medication models)• Mapping to different host systems
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Fixed and Default Values
• Provide support for generic processing
• Cost is “ugliness” and “low data density”
• Implementers not keen to access separate definitions for every message type
• Need to explore name stability strategies
• Impact on related sets of messages, and versioning of messages over time
• HL7v3 as storage format…
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HL7v3 XML as storage format
• HL7 does recognise this as a requirement for CDA documents (persistence)
• Is a requirement for store-and-forward systems, and there is a continuum between these and registries
• Registry interfaces that address non-functional requirements must address this issue
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CEN / HL7 harmonisation
• Reference Model – Datatypes…
• Reference Model – Structural…
• Constraint Mechanisms…
• Wire Format (to be continued)
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CEN / HL7 harmonisation
• Reference model– Proposed UML ITS datatypes a potential common
datatype solution– Issues between Clinical Statement and 13606 to be
explored
• Constraint Mechanisms– HL7 refinement process/CMETs/Templates/Vocab
and archetypes achieve equivalent constraints– Interchangeable representations (some minor
differences in expressivity, mainly tool related)
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Outstanding Requirements Issue
• What’s the use of element names?– Maybe to infer some fixed/default values– What xPaths do folk want to write?– What criteria should be used for name
stability between models and versions?
• More issues after the introduction of the ITS proposals
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Abstract R2 Datatypes issues
• Propose R2a and R2b releases
• The following Null Flavors to be removed and consequent problems resolved– Other, TRC, SQ– PINF, NINF
• II.usecode to be added
• CD.group to be added
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Methodology changes
• *Ensure that there are business names for every class in a RMIM
• Syntax to be proposed for datatype component constraint
• Enable explicit constraints for infrastructureRoot attributes
• *Add the ability to indicate that a class can/must/must-not be included by reference in the instance (eg ActRef)
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New ITS Proposals
• For every RBM create a UML model and XML Schema – these will be called the XUM (XML UML Model) in this presentation
• The XUM will be normative• The UML and XML Schema expressions of the XUM
with be equivalent• The XUM will be expressed as a mix of rules
(ocl/schematron) and structure• There will be a reference package of datatypes and
enumerated types• There will be a secondary UML representation using the
XML for UML profile from http://www.xmlmodeling.com to make the XML-UML mapping explicit
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New ITS (cont)
• The XUM will not include fixed and default values in the wire format (a more general model should be used as a basis for serialisation if this irritates)
• The XUM will collapse nested classes to some extent
• Because there is a XUM for every RBM, there can be serialisation at any level of specificity (see issues)
• If template assertions are included then they cannot be validated by XML schema (as for the XML ITS)
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Issues
• Governance for which model in a hierarchy to use to serialise
• What are the guidelines for inheriting names from a parent model?
• What happens at model boundaries?
• Should we use business names in instances?
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Examples
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Next Steps