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Subject: Re: [ubl-dev] Re: Code list extensibility and substitution groups
On Tue, 22 Feb 2005, Stephen Green wrote: >> >>As an aside, wouldn't it be a plausible argument against substitutionGroups >> that folk like myself, not expert in >>XSD but likely to be responsible for implementations nonetheless, would >>find substitutionGroups a little perplexing (even if just for failure to >>see their value in this context and therefore reluctance to invest >>adequate time into adopting them). >>I think my own Government's XSD guidelines are to avoid the more >>obscure aspects of XSD in Schema architecture, perhaps for related >>reasons. The presence of substitutionGroups can also create a sense of "the element is not the type which it's present manifest type suggests" -- in other words, what type you see that's associated with an element at present may not be what is being used for validation. The situation would be worsened if the actual substitution definitions come in from another <include>d file stored physically elsewhere, and might also introduce possible authenthicity issues (eg. allowing validation using bogus subsituted groups when invalid codes exist in instances). This is not to say that the mechanism of XSD substitionGroup itself is not good. But in the context of UBL and general environment of business document exchanges, many other factors and considerations come in (many of which experts from various fields have pointed out). A more stable, easily understood, and reliable expression of schema that serves as pillar on which to build high-level validations and functions would likely be more useful in practice. Best Regards, Chin Chee-Kai SoftML Tel: +65-6820-2979 Fax: +65-6743-7875 Email: cheekai@SoftML.Net http://SoftML.Net/
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