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Re: what's wrong with using XML Schema/HTML/RDF to document namespaces?

From: Dan Connolly <connolly@w3.org>
Date: 10 Dec 2002 11:02:49 -0600
To: Tim Bray <tbray@textuality.com>
Cc: www-tag@w3.org
Message-Id: <1039539769.5318.12562.camel@dirk>

On Tue, 2002-12-10 at 00:46, Tim Bray wrote:
> Dan Connolly wrote:
> > I invite folks to use this namespace
> > name in their documents:
> > 
> >   http://www.w3.org/XML/2000/04schema-hacking/my

[oops; I chose a poor example; I thought this
was an example schema, but it's also an example
unrelated HTML document... I managed the
namespace poorly... ok, the my.html is gone
now...]

> > 
> > If you GET that thing, you'll find
> > an XML Schema document which allows
> > a machine to distinguish a syntactic
> > subset of XML documents that are
> > consistent with my expectations.
> > 
> > Why is that not OK?
> 
> When I open it in Mozilla, I get a blank screen. When I open it in IE, I 
> get a bit of HTML which I am willing to grant, for the purposes of this 
> experiment, could be useful information about the namespace.

I don't intend anything interesting to happen when you open it with
a web browser. When I gave you the pointer, I told you it
was useful for XML Schema validation; I don't know why you would
expect it to be useful for anything else. When I invite folks
to use that namespace name, I set expectations accordingly.

Now if you happened upon that address out of context, you
can still view source and follow your nose thru namespace
pointers and such...

Inside 2000/04schema-hacking/my, you'll
find...

<schema xmlns="http://www.w3.org/1999/XMLSchema">

and if you follow that pointer, you'll find
the schema-for-schemas there; sort of a terminal
node. Hmm... it seems to be missing a pointer
to the then-current schema spec...

  http://www.w3.org/TR/2000/WD-xmlschema-1-20000922/

That's a bug; but I don't think it's critical to
my argument.

>  What is 
> the intended effect?

The intended effect of the documentation I put there is,
as I said, "to distinguish a syntactic
subset of XML documents that are
consistent with my expectations".


> I stand by what I said in http://www.textuality.com/tag/Issue8.html and 
> I think that it would be helpful if you'd address some of the arguments 
> in there.

I don't see anything in there that argues against what I've done.

 1. It is not strictly necessary for namespace documents to exist.

no problem there.

 2. Namespaces vary widely in semantic effect.

check.

 3. Namespaces have definitive material.

yup.

 4. It is good for namespace documents to exist.

agreed...

 5. Namespace names should not be relative URI references.

I think relative URI references should work fine, but I haven't
used them anywhere in these examples, so... check.

 7. The definitive material for a namespace is normally distributed
among multiple resources.

well, in these cases, yes and no: there's one definitive piece
of documentation to start with, so in that sense, no. But
that starting document's meaning is a function of other documents.
So yes.

 8. Content-negotiation is not a sufficiently powerful tool for
selecting definitive-material resources.

I'm not using content negotiation in any of the three
examples I gave.

 9. Namespace documents should provide a level of indirection.

In these cases, there's only one thing to find, so step 2
of your argument supporting this point doesn't apply
  "# Such definitive material is usually found in more than one
resource."


> An XML Schema is highly architecturally unsound because it is (a) by 
> default not human readable,

Hmm... it seems to be as human readable as, say, an SVG document,
or even HTML; if you have schema visualization tools, you can
make sense of it. If not, you can follow-your-nose to
natural langauge documents that explain, to the satisfaction
of a wide technical audience, what it means.

>(b) presupposes a highly controversial 
> choice among several alternatives thus precluding them,

I think this is a spurious argument... I am *NOT* saying
that
	For every namespace name, the result of dereferencing
	that namespace name is an XML Schema.

I'm only saying that

	For some namespace name(s), the result of dereferencing
	that namespace name gives you an XML Schema.

Surely I, as namespace designer, get to choose what format
to use to document my namespace, no?

I chose 3 examples (XML Schema, RDF, HTML) to illustrate
that I expect different namespace designers to choose
different formats to document their namespaces.

>(c) suggests 
> that schemas are more interesting or useful than other kinds of 
> resources,

In the 2000/04schema-hacking/my case, yes; as namespace designer,
I've decided that the most useful thing to use to document it is an
XML Schema.

Are you saying that's *never* the case?

In other cases, we chose HTML or RDF. Are those *never*
acceptable?

> and (d) has no default way to look up other useful things 
> that aren't XML schemas.

Yes, it does: annotations; specifically, the source
attribute on appinfo and documentation.
http://www.w3.org/TR/xmlschema-1/#cAnnotations


>  Bah. -Tim

I remain unconvinced.

-- 
Dan Connolly, W3C http://www.w3.org/People/Connolly/
Received on Tuesday, 10 December 2002 12:02:38 GMT

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