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

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  • From: "Simon St.Laurent" <simonstl@simonstl.com>
  • To: Dan Connolly <connolly@w3.org>
  • Date: Fri, 19 May 2000 10:47:12 -0400

At 02:52 AM 5/19/00 -0500, Dan Connolly wrote:
>I'm happy to leave "meaning" aside, but you must grant me that
>a schema is descriptive of a namespace, no? That is: if
>I have a Web of documents, and in each document, each
>term in its markup vocabulary refers to another document
>that describes that vocabulary (possibly with reference to other
>documents), such a Web is self-describing, no?

A schema _can_ be descriptive of a namespace, but is not necessarily
descriptive of a namespace.

>> This is a note, one of a series of documents that claim no official
>> endorsement from the W3C,
>Right... it just explains the direction we're headed in when we
>charter new work and such.

Perhaps, although it seems you're making a distinction between Notes we
wrote and like, and everyone else's Notes, which supposedly have no
normative value whatsoever.  This is a new distinction, at least in public.

>> and one whose claims are contentious.


>I believe this issue has been discussed before, without an overall
>conclusion... it seemed to get as far as "you can't do that...
>you need packaging to do that" vs. "packaing is fine, but
>it's not critical path to using schemas and namespaces".

Without public archives, I have no way of knowing this - it doesn't exist
for the terms of this public discussion.  Sorry.

>But now we have a schema implementation in development, and
>I'm trying to use it to show that using namespaces
>and schemas works just fine. By all means, let's do
>discuss it, now that we have more specifics
>to work with.

It works just fine - for the narrow set of purposes you appear to be
interested in. It's far from clear that the usage you propose is good for
the wider set of cases I'm interested in, and it's quite clear that the
usage you propose is harmful to certain cases.  'Blessing' namespace URIs
as pointers to schemas gives that usage an imprimatur that makes it
difficult for them to be reliably/interoperably used in any other way.

>Umm... you mean nobody is doing experimental design nor implemention?
>Nobody's doing any hacking or anything? I sure hope they are;
>as Linking finishes up and we find more time to devote to packaing,
>I hope there are proposals on the table so that we don't have
>to start from scratch.

It comes up on XML-Dev fairly regularly.  I gave a presentation on one
possibility last August in Montreal:

More details at: http://purl.oclc.org/NET/xpdl

(No, I didn't call it 'packaging', as I started before that term came into
>>[...documents with no schemas...]
>I don't see how that represents a problem;
>had no schema (i.e. nothing more than a prose description as a schema)
>for quite some time with no problem. So did dublin core and lots
>of other namespaces.
>Could you give more details on how this scenario is a problem?

If software starts expecting schemas at the end of a namespace URI, it may
lose the ability to process documents for which that is not the case (or in
which don't use namespaces).  More functionality, perhaps, but less

>> b) will be using DTDs, XDR, RELAX, or some other schema approach in
>> addition to or in place of XML Schema.
>Again, I don't see how this is a problem. Making an XML schema available
>at http://www.w3.org/XML/1998/namespace in no way interferes with
>use of RDF schemas for http://www.w3.org/1999/02/22-rdf-syntax-ns#
>nor with use of RELAX for other namespaces I've seen.

Putting a schema there has no direct effect, except inasmuch as it
represents the W3C blessing the practice of putting XML Schemas at the end
of a namespace URI.  This creates similar problems for processors expecting
one thing and getting another.  Given the current state of MIME types and
content negotiation, the infrastructure for avoiding these cases (which you
suggested) is rickety at best and dangerous at worst.

>I doubt many namespace designers will find it useful to use
>more than formal mechanism (DTDs, XDR, RELAX), but even
>that is feasible using different MIME types or perhaps
>different namespace parameters on the text/xml MIME type.

'Namespace designers'?  Is that a new title?

Actually, I'm encouraging people who build schemas to have DTDs as well,
and possibly RELAX or XDR depending on their needs.  XML Authority makes
this awfully easy.

>And of course, anybody who is unable, unwilling, or just
>uncomfortable with depending on HTTP content negotation
>is welcome to ask their users to use schemaLocation
>in stead. 

I'd recommend that to _everyone_ at present.

>But at W3C, we have experience using content negotiation
>to evolve from GIF to PNG and so on, and so I'm comfortable using
>it to evolve markup descriptions of markup vocabularies
>from HTML to XML.

I'm not comfortable (is anyone?) recommending that practice to anyone else,
however, and the W3C's use of it seems rather ahead of its time.

>> Managing that requires more than pointing to a schema.
>I believe we've shown by demonstration that this is not true.

Demonstration, please.

>Could you explain how it is that what we're doing (i.e. the
>schema validator that uses namespace names to find schemas)
>doesn't work?

It works great for the schema validator.  It's a train wreck for the rest
of us.

Simon St.Laurent
XML Elements of Style / XML: A Primer, 2nd Ed.
Building XML Applications
Inside XML DTDs: Scientific and Technical
Cookies / Sharing Bandwidth

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