At the moment, all the attributes of DV_IDENTIFIER are mandatory. In health care none of the features other thant the ID are used at present - at least in HL7 v2. Although we could use empty strings, the problem is that people doing transforms feel they have to debate what to put into each. Making them optional is a much more suitable response and would provide backward compatibility. It will mean we need to have a way of saying that a feature is mandatory in the archetype.