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Null (in HL7) could refer to:
- A special value defined in the HL7 version 2 to denote the value "known to be empty", expressed in v2 syntax as "" (two double quotes without content)
- The concept of nullFlavor in HL7 version 3 to identify "the reason for not sending a normal value".
- Q: What's the equivalent in HL7 v3 of the null in v2 (|""|)?
- Answer: <attributeName updateMode="D">, provided one uses updateMode (which is only used in selected attributes in selected domains right now - it is not available as a generic mechanism for all attributes in v3). Details on updateMode can be found in the Core Principles document.
- Q: so why is there no v3 "nullFlavor" which corresponds with the v2 null? v2 only has one null, and v3 has a whole bunch of them, sureley there is an equivalent?
- Answer: although they share a similar name, the nature of the v2 null (known to be empty, if you already have data, please delete it from your database) is different than the nature of the v3 nullFlavors (reasons why you don't know the value of the attribute)