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RE: [xml-dev] XML spec and XSD

> I don't know, how a technology (i.e, XSD..) that is capable 
> of doing XML validation (and XSD does this well), and is 
> implemented by number of XML products, which is implemented 
> widely in XML applications (I can see uncountable XML 
> instances been validated by XSD every day), can be damaging.

I think Simon is probably thinking in terms of opportunity costs. That is,
the idea that if this technology hadn't been so widely adopted, the
community might have adopted something better instead, and gained a better
return on its investment.

He might also be thinking that for some people who have adopted the
technology, the cost has been greater than the benefit. I think it would be
hard to demonstrate that objectively.

> I am asking only for a simple reference in the XML spec, 
> pointing to the XSD spec and ideally saying somewhere in the 
> XML spec (2.0 perhaps), that XSD is another validation 
> technology from W3C similar to DTD.
> I still cannot think, why anybody can disagree to this. XSD 
> and DTD both belong to W3C, and both are W3C recommendations, 
> so I don't think why this simple modification to XML spec 
> cannot take place.

We're dealing here with specifications: a legalistic contract between the
implementor of an XML parser and the user of an XML parser. You can write a
fully conformant XML parser without ever knowing that XSD even exists.
Furthermore, you can use XML without ever knowing that XSD exists.
Therefore, XSD doesn't need to be part of the XML contract. Equally, you
wouldn't want XML to be mentioned in the Unicode specifications, because
Unicode has no dependency on XML, and would still be of value if everyone
suddenly decided to abandon XML and move to YML instead.

It's of great value that specifications should NOT have unnecessary
dependencies. The fact that XML links normatively to DTDs is undoubtedly a
bad thing. In this respect the architecture of specifications is very like
the architecture of software implementations: you want the components to be
as loosely coupled as you can achieve, to allow each component to evolve or
to be replaced with minimum impact on the other components.


Michael Kay


Michael Kay

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