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Subject: Re: [ubl] Discussion of substitution groups
I believe we need to use substitution groups for minor versioning as per NDR Rules VER 8 and VER 9, to allow use of imports of previous versions' schemas and xsd derivation. I believe this has been an important part of the NDR design from the beginning of UBL, it having been intended since then that minor releases and customisations would use XSD-enabled inheritance and polymorphism. The reason the above requires substitution groups to make it work in UBL is the highly structured, type oriented and essentially complex nature of UBL. I believe it would be impossible or at best far more difficult to achieve the same aims with a local schema design, This, I believe, was the main reason for the use of the global element and global type design. I also now believe it would be impossible or very difficult to achieve the same goal using XSD redefine (or any other XSD method for that matter). (IMO) the only choice might be whether to use abstract elements and types, forcing substitution and I see nothing to be gained and much possible confusion from this so I personally would rather avoid it, as we did with the design we recommended to the TC from the UBL minor versioning [ver] working group in April. Thankfully, Marty has well demostrated that a working design for substitution group use without abstracts can be used for codelist extension too. Overall, in just a few words, we need it for XML with XSD to be properly eXtensible in UBL. All the best Steve ----- Original Message ----- From: "CRAWFORD, Mark" <MCRAWFORD@lmi.org> To: "Stephen Green" <stephen_green@seventhproject.co.uk>; <ubl@lists.oasis-open.org> Sent: Monday, July 18, 2005 4:08 PM Subject: RE: [ubl] Discussion of substitution groups > This all the more persuades me that for > minor versioning and codelists we have > only one sensible option - substitution > groups (without use of abstracts). But if our schema follow our NDRs and are created from models as expressed in the spreadsheets, why do we need to use substitution groups at all?
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