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