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   RE: [xml-dev] Who can implement W3C XML Schema ?

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Welcome to the world of design by committee. You can say the exact same things about C99, C++ and SQL92 which have had 3, 5 and 10 years respectively for smart people to implement but still are full of quirks, issues and distinctions between competing implementations.  I'm sure more experienced and knoowledgeable people than me can add more names to this list (perhaps CSS and HTML?) 

	-----Original Message----- 
	From: Paul Spencer [mailto:paul.spencer@alphaxml.com] 
	Sent: Wed 3/20/2002 3:06 AM 
	To: Eric van der Vlist; xml-dev@lists.xml.org 
	Subject: RE: [xml-dev] Who can implement W3C XML Schema ?

	> I begin to be really worried about the "implementability" of W3C XML
	> Schema and I'd like to give an example of what I have already
	> experienced several times in the past months (I insist that this is an
	> example and almost the general case, *not* an exception).
	I have to agree. I keep coming across schemas that validate in one tool, but
	not in another. Sometimes the schema is valid but wrongly described as
	invalid, other times it is invalid but the errors are not detected. In one
	case, I was asked to look at a schema, and a tool detected an error, but
	missed the identical error elsewhere in the same file. I have yet to find
	any tool that correctly identifies all errors without also indicating false
	errors. And this is on relatively simple schemas.
	We do a lot of schema development and test all schemas against three of the
	popular validating tools before delivery. This way we try to catch the
	errors and to work around the constructs that generate false errors. But, of
	course, many here will be aware of one particular tool that gives different
	false errors depending on whether you are looking at the schema in a
	graphical view or as text. They don't make it easy for us ...
	The guys that write these tools are not stupid. If they haven't got it right
	by now, I worry for the future of XML Schema.
	Paul Spencer
	CTO, alphaXML Ltd
	Author: Professional XML Design and Implementation (Wrox Press)
	Co-author: Beginning XML, Professional XSL (Wrox Press)
	XML services for Industry and Government
	+44 (0)1491 630053
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