W3C home > Mailing lists > Public > xml-uri@w3.org > May 2000

Re: Thoughts from an external observer

From: Eric van der Vlist <vdv@dyomedea.com>
Date: Tue, 23 May 2000 15:38:43 +0200
Message-ID: <392A89E3.3ADF1470@dyomedea.com>
To: xml-uri@w3.org
David Carlisle wrote:
> > I would have expected at least some acknowledgment
> Sunday afternoon? Was sowing vegetables in the allotment, there are more
> important things in life than XML you know:-)

I haven't been able to go to our country house last Sunday ;)
> > 3 examples of applications doing so have been mentioned so far :
>    <RDF xmlns="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
>                        xmlns:DC="http://purl.org/dc/elements/1.0/">
>    <Schema name="Schema" xmlns="urn:schemas-microsoft-com:xml-data"
>     xmlns:dt="urn:schemas-microsoft-com:datatypes">
>      xmlns:math="http://www.jclark.com/xt/java/java.lang.Math"
> All those examples use absolute URI so arguably are out of scope for the
> discussion, but they do usefully show how other specs can usefully use
> the namespace URI for whatever purpose they want, including retrieving
> stuff, but do it in ways that don't break the primary use of namespaces
> which is to give a structured name to XML constructs, with a name
> consisting of a pair (URI reference, XML 1.0 Name).

But if nobody was using namespace URIs to retrieve anything, the
discussion would be academic...

I also wanted to point out a confusion since many posts are speaking of
"schemas" and it took me a while to separate RDF schemas from XSchemas. 

> > Are the applications supposed to guess if they will find a XSchema, a
> > RDF schema or anything else when they follow the URIs ?
> Quite, which is why a schema validator ought not follow a random
> namespace URI in a document. An xpath expression evaluator, if it sees
> math:sin( knows that the prefix is being used in an extension function
> so can look up the URI reference bound to the prefix and choose the
> appropriate class. Its interesting to note that saxon's version
> of this allows absolutely any URI at all
> xmlns:math="what/ever/you/like/java.lang.Math"
> would work. If the prefix is used in an extension fuction the last
> component of the URI reference bound to thet prefix is used as a
> java class name. I have no idea what a schema validator would make
> of such a document if it tries to follow such a URI, it could find
> anything at all (nothing most likely). Having a schema validator
> follow namespace URIs has no virtues at all as far as I can see.

It seems to have a virtue for RDF schemas, though.

> > Why couldn't we follow the suggestions to keep the namespaces as a
> > mechanism to disambiguate names and add a separate mechanism to link the
> > resources associated with the namespace ?
> We could follow that suggestion. We should.
> > If we accept relative URIs (from my reading of the various specs) in
> > addition to what has been said about XPath, the xslt processors will
> > need to be updated to change the namespace in the output tree.
> You mean here if we accept the change to make URI refs absolute .

I meant in the "OPTION 2" as defined by Joe Kesselman :

>> References "writ large". If an author writes a relative URI, applications
>> see it only in its absolutized form, after being combined with the base URI
>> in effect at that point in the document. Note that a single document may
>> have multiple base URIs, due to the use of external entities; the XBASE
>> proposal raises the same possibility.

The other options do not have this impact, you're right.


Eric van der Vlist       Dyomedea                    http://dyomedea.com
http://xmlfr.org         http://4xt.org              http://ducotede.com
Received on Tuesday, 23 May 2000 09:37:29 UTC

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