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Andrew, I particularly liked Dave Orchard's exposition of the problem and the partial solutions. In XForms we allowed foreign attributes across the board, added an <extension> element, and added an attribute mustUnderstand (borrwed from SOAP) to let document authors express which extensions are required and which ones are optional. It still doesn't feel right, since the <extension> element is clunky, and the division line between Schema author and document author seems inadequate if there are multiple document processing contexts. The analysis in Dave Orchard's paper shows, however, that nothing (yet) feels quite right. I think it really *ought* to be easy to define a language that allows extensions from other namespaces, specifies where they are allowed, and maybe even lets you (the Schema author) say something about the extensions as substitution groups do, but without having to dance through the minefields of optional elements and sequence limitations. In my non-Xerox time I am trying to help design a language that allows for future extensibility, and finding the tools still a bit blunt (http://xdif.org). Leigh. -----Original Message----- From: Andrew Wheeler [mailto:akwheel99@h...] Sent: Tuesday, October 26, 2004 11:12 AM To: xml-dev@l... Subject: Schema Evolution ... [3] Providing Compatible Schema Evolution. http://www.pacificspirit.com/Authoring/Compatibility/ProvidingCompatibleSche maEvolution.html
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