Re: [xml-dev] The purpose of a namespace URI is ...

[Dan Vint <dvint@dvint.com>]

I guess I'm using the notion/idea of Public Identifier as a unique 
string and a string that has version information so I can identify 
exactly what that document conforms to. I don't necessarily see that 
as the same thing as the namespace identifier but that is the only 
thing that the schema designers have given me to use.

In the previous message you pointed out attributes of the PI that I 
know existed but I'm not sure anything ever used that for more than 
identifying a DTD. PIs were probably needed in XML to preserve 
documents that were SGML and only had PIs to identify them. They 
could have easily been incorporated into Schema, but it wasn't so we 
lost the functionality provided (versioning anyway, not everything 
else you pointed out).

So currently I'm left with a mechanism that is overloaded and maybe 
not adequate for all the uses. That then compounds with not having a 
standard mechanism for supporting versioning that works in schemas 
and catalogs that general applications can implement consistently. 
Changing the URI is the only mechanism I have for managing this. I'd 
welcome a standard mechanism for doing this, but I'm still left with 
legacy schemas that I would have to deal with.

..dan

At 10:34 AM 12/2/2012, Liam R E Quin wrote:
>On Sun, 2012-12-02 at 09:33 -0800, Dan Vint wrote:
> > This is an ok alternate way of getting the same effect, but it is not
> > supported universally. For instance XML catalogs I don't believe will
> > work with this.
>
>That's an interesting point. It would be an interesting idea to augment
>XML Catalogue files with the ability to discriminate based on a version
>attribute, although I don't think that would fit well with all existing
>APIs for entity resolvers.
>
>The truth is that we had very little time available when we designed
>namespaces, and some of the people involved were not up to speed with
>Web architecture.
>
>However, there's no intrinsic advantage to a public identifier over a
>namespace URI, they're both strings; the Web has been described as an
>experiment to find out what happens if you give everything a name, a
>URI, and so at W3C there tends to be a lot of pressure to use URIs for
>everything.
>
>[...]
>
> > The Public Identifier provided a good mechanism for identifying the
> > vocabulary of a document, why was this not carried forward with Schemas?
>
>The battle you should fight is not public identifiers vs. URIs. That
>battle has basically been fought more than a decade ago, and, like most
>battles, happened because the people involved failed to reach agreement.
>We should not have included public identifiers in XML at all - it would
>have been better than including them without defining how they worked,
>when SYSTEM urn:foo has the potential to be just as good and SYSTEM
>http://... had the potential to be better.
>
>Maybe Oasis (or even a joint Oasis/W3C group?) could enhance XML
>catalogs to support simple conditional mappings, but I'm not sure if the
>changes would get enough traction today to be worth while.
>
>I agree that when you have, for example, a mixture of XSLT 1 and XSLT 2
>and XSLT 3 stylesheets and you want to feed them to different
>processors, the namespace identifier is not adequate. Neither, however,
>are public identifiers on their own, since by the time an XSLT processor
>is resolving a PI, you've already chosen an XSLT processor... so the
>logic belongs in whatever you are using to choose the XSLT processor.
>
>Maybe this would be a good requirement to bring to the XML Processing
>Model Working Group.
>
>So there are multiple use cases for versioning, and no single answer,
>except that more could be done.
>
>Liam
>
>--
>Liam Quin - XML Activity Lead, W3C, http://www.w3.org/People/Quin/
>Pictures from old books: http://fromoldbooks.org/
>Ankh: irc.sorcery.net irc.gnome.org freenode/#xml

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