Re: [ubl] How UBL could postpone a decision about whether or not to implement the CLSC Codelist Schema Design

[jon.bosak@sun.com]

So here's the way things look to me this Monday morning:

 - There are doubts in the XML expert community about the wisdom
   of using XSD substitution groups in general

 - We suspect that there may be parsers in current use that don't
   support substitution groups (though I don't think we've
   confirmed this)

 - Some people in UBL are firmly of the opinion that substitution
   groups are unacceptable for business use

 - Some other people in UBL are not quite so firm in opposition
   but are not comfortable with the idea of ad hoc additions to a
   schema even though we are well aware that many users consider
   ANY a feature

 - The NDRSC long ago considered the use of substitution groups
   and ruled them out of play for 1.0, so introducing them at this
   point will require an exception for code lists; this is not
   impossible, but it would require us to revisit the rationale
   for excluding substitution groups and explain why that
   rationale does not apply in the case of code lists

 - We have not been able to confirm that the mechanism proposed
   for code lists can be implemented in constraint languages other
   than XSD (W3C), in particular ASN.1 (ITU) and RNG (ISO)

 - Stephen Green has proposed a plan for implementing code lists
   in a way that avoids the use of substitution groups for 1.0 but
   allows for this method to be included in 1.1 without breaking
   backward compatibility with 1.0 instances:

      http://lists.oasis-open.org/archives/ubl/200403/msg00086.html
      http://lists.oasis-open.org/archives/ubl/200403/msg00095.html

If Stephen is right, then clearly the only prudent course of
action is to adopt his solution and consider the addition of
substitution groups for code lists in 1.1 when we have resolved
the uncertainties listed above.  So the question of the day is
whether Stephen's approach will work.  If no one can show him
wrong by the time we discuss this Tuesday (7-9 a.m. California
time) then I'm going to have no choice but to strongly urge what
on the face of it appears to be the safest course of action.

Jon