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V2 Lengths

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Revision as of 14:27, 19 August 2008 by Shaver (talk | contribs)
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Background

  • long controversy concerning lengths
  • lack of clarity concerning what we are trying to do
  • problem of the back door

Solution

  1. stop reporting lengths on complex types
    • value is increasingly difficult to determine
    • value is specific to vertical bar representation
    • value is useless and misleading
    • only define lengths for primitive types (ST etc)
    • only report lengths were the context of use has different rules to definition of type
  1. differentiate between authoritative lengths and arbitrary lengths
  • some lengths are authoritative
      • codes fixed by HL7
      • segment/field references
      • realm fixed value in a realm specific message
    • authoritative lengths are fixed and normative - may not be violated
    • systems must support valid data that they encounter
  • some lengths are arbitrary - any particular length is wrong
      • lengths of codes and names, address parts
    • Do not make normative rules. But some length guidance is still useful
    • so provide a "conformance length": the minimum length that must be supported
    • conformance length offers a degree of predictability without preventing real world problems being solved
  1. add support for truncation pattern
    • truncation behaviour exists in the wild
    • it works better if systems are able to communicate about truncation
    • truncation allows this.
    • truncation pattern is not required
    • some content (identification, clinical descriptions) are not allowed to be truncated
    • some data type specific truncation rules (numbers, dates)