HL7 use of UIDs

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