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HL7 Use of UIDs & ISO WI: Object Identifier Needs and Feasibility

This article discusses the use of UIDs in HL7 and ISO WI, including the need for globally unique identifiers, the creation and availability of master and local copies, and the feasibility and efficiency of fixed length UIDs. It also explores the challenges and potential conflicts in using UIDs in the context of DICOM and HL7 Version 3 interoperability.

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HL7 Use of UIDs & ISO WI: Object Identifier Needs and Feasibility

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  1. HL7 use of UIDs & ISO current WI Nicholas Brown DICOM WG 10 London 2003

  2. Object identifier needs • Which it is (globally unique) • Who created it • Where the master copy is to be found • Where a local copy is available for rapid access • ‘Which’ and ‘where’ may be combined into one field but this is not thought to be a good idea by some but may not be too bad according to Fred!

  3. HL7 Ver 3 Provision & text 1 • Defines UID data type • 2 main fields called • Root • Extension • Implied use: extension is locally unique user friendly identifier. If absent root is the UID. If present concatenate root and extension to obtain globally unique ID

  4. HL7 Ver 3 Provision & text 2 Text description makes clear that the specification of root is as a globally unique identifier such as used by DICOM. In particular it says that semantics may be inferred but that this use is not supported by HL7 • Woody keen on use of GUIDs - 128 bit UIDs in Hex as used by Microsoft.

  5. HL7 Ver 3 Provision & text – problems ? • Maybe precludes the use of a globally unique UID such as DICOM uses and a locally unique user friendly ID ?? • Length not defined • (HL7 lengths are only recommended not mandatory) • Format not defined • Multiplicity? (maybe allows global and local) • How use Ver 3 to support need for 3 UIDs to identify and access a DICOM object?

  6. Current ISO WI for exchange format for UIDs • Explain use of UIDs • Feasibility and efficiency of fixed length • Justification for separating ‘which is it’ from who created object and where it can be found • Propose • 64 char alphanumeric string (supports 64 char DICOM and 32 char GUID) • Separator to be period • No leading or trailing spaces etc (current ISO logical only)

  7. HL7 view • Strong opposition to fixed length • Need to support customer request to combine ‘which is it’ and ‘where/who’ much more than 64 chars. • Combining classical ‘root’ and free format for local ID is a neat idea.

  8. IHE use of HL7 and DICOM • Conflict in use of UID may pose serious problems for interoperability of DICOM and HL7 Version 3 • Ver 3 ideas not yet tested in the real world

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