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   Toward the self-describing web [was: Irony heaped on irony]

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  • From: Dan Connolly <connolly@w3.org>
  • To: "Simon St.Laurent" <simonstl@simonstl.com>
  • Date: Thu, 18 May 2000 09:20:56 -0500

[xml-uri folks: thread starts with
From: Tim Bray  <tbray@t...> 
Date: Wed May 17, 2000 5:08pm 
Subject: Irony heaped on irony">mid:
availble at http://www.egroups.com/message/xml-dev/20401?&start=20399
and in http://xml.org/archives/xml-dev/xml-dev.200005 ]

in which Tim Bray wrote:

The namespaces rec hardwires the prefix "xml:" to the namespace
               http://www.w3.org/XML/1998/namespace - until recently, if
               that URL, you got a nice helpful human-readable note
saying "this
               is for XML, go check out http://www.w3.org/XML and <a
couple of
               other useful
               pointers which I forget>".

               Today, I went and looked at it, and there is now some
sort of XML
               fragment there which is unreadable in MSIE5 because of an
IE5 bug,
               unreadable in the NS6 beta because there's no stylesheet.
               seems to be limited to providing declarations for
xml:lang and

               I'm wondering if this is a step forward. -Tim

I agree that it's unfortunate that we lost the HTML functionality
when we put the schema there... I'm hacking the necessary
content negotiation support in the schema validator so that
it will ask for XML in preference to HTML so that I can
put the HTML thing back.

and then...

"Simon St.Laurent" wrote:
> At 10:05 AM 5/18/00 +0100, Henry S. Thompson wrote:
> >This is my 'fault', I guess, although it seems to me it's a problem
> >with the browsers you mention in the first instance.
> [...browser issues]
> >I could move the schema, but that would break lots of _other_
> >schemas, including the schema for schemas, which depend on it.
> >
> >Seems to me having something of mime type text/xml at the namespace
> >URI for XML is not something we should have to apologise for.
> But it does seem that such a sweeping change in namespaces best practices
> is worth an explanation or preferably a full-blown trip through the W3C
> process, complete with working drafts.

Change? From what? The best-practice for Web resource identifiers
has always been that you can use them to access some representation of
state of the resource they identify, no? And namespaces are
resources just like tech reports, images, and other sorts of
documents and services and such, no?

Disambiguation of names is a critical feature of XML Namespaces,
but what really makes it powerful and useful is that it makes the
web of XML documents self-describing: whenever you get a document,
you should be able to use the namespace identifiers to figure
out what the author of the document meant by the vocabulary
of tags and attributes used in the document.

We have documented this since Feb '98, when XML 1.0 became
a recommendation despite the lack of namespace support:

	"Therefore it is essential that when a document is written to
	refer to a namespace, the name space definition should be a 
	generic resource whose instances may include schemas in various
	languages at various levels of sophistication.  This is an
	essential growth point for the web. "

	-- http://www.w3.org/TR/1998/NOTE-webarch-extlang-19980210#Evolving

It's an essential component of the architecture of the Web that
we're working toward:

	The namespace document (with the namspace URI) is a place for the
	language publisher to keep definitive material about a namespace.
	Schema languages are ideal for this. There is a huge a mount of
	value to be gained from having a document be self-describing in
	the Web. (This does not preclide the operation of checking a
	document against a different schema if one wants to as a local
	operation). The first stage in self-describing documents is to
	do it at the XML schema (structure) level. Successive stages are
	to give semenatic information.

	-- http://www.w3.org/DesignIssues/Architecture

> We've spent over a year on XML-Dev and elsewhere explaining to the world
> that Namespace URIs are just identifiers,

Surely the fact that Namespace URIs are identifiers is not exclusive
with using those identifiers to access definitions of those identifiers,
is it?

I'm well aware of the bit from the namespace spec...

	"The namespace name, to serve its intended purpose, should have
	the characteristics of uniqueness and persistence. It is not a
	goal that it be directly usable for retrieval of a schema
	(if any exists)."

	-- http://www.w3.org/TR/1999/REC-xml-names-19990114/

but surely that applies just to the namespace spec, not to specs
layered on top of the namespace spec, e.g. RDF Schemas, XML Schemas,
my-favorite-namespace-use etc.

I think that sentence gets exploited to suggest that it's OK
to use http://example.org/foo as a namespace name and then
allow 404s for requests to that address, and so we should
take it out if/when we next revise the Namespace spec.

It's perfectly reasonable to use
as a namespace name to relieve yourself the burden of running
an HTTP server, very well. But if you use http to identify
a resource, you set an expectation that you'll service
that address on demand.

> battled over the three/one
> namespaces for XHTML issue, and now it seems that namespaces are indeed
> supposed to point to schemas.  (And packaging?  Is that gone?)

Packaging isn't gone; it's still on the TODO list

But I don't see how it's a necessary predecessor
to making an XML Schema available as "definitive material" about
http://www.w3.org/XML/1998/namespace .

> Maybe the xml-uri list is the place to bring up such questions,

Yes, please.

> though it
> seems obsessed with relative URIs.
> Simon St.Laurent

Dan Connolly, W3C http://www.w3.org/People/Connolly/

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