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Re: RDF in XHTML [was: Re: Authors describing what their URIs mean]

From: Murray Altheim <altheim@eng.sun.com>
Date: Mon, 16 Apr 2001 02:34:53 -0700
Message-ID: <3ADABCBD.B2A55519@eng.sun.com>
To: Joshua Allen <joshuaa@microsoft.com>
CC: Seth Russell <seth@robustai.net>, Danny Ayers <danny@panlanka.net>, "Sean B. Palmer" <sean@mysterylights.com>, RDF Interest <www-rdf-interest@w3.org>
Joshua Allen wrote:
> 
> > I long ago gave up proselytizing validation; if you don't feel it's
> > important, go right ahead and create well-formed XML. I find
> validation
> > in most instances to be worth the trouble, like I find a Java debugger
> > helpful. If you've got an XHTML plus SVG document and its acting up,
> > I hope you have a DTD.
> 
> On the other hand ... the XHTML DTD certainly does not provide
> assurances that the script contained in a <script>..</script> block is
> valid, nor does it give you any help when debugging the CSS in your
> <style>...</style> block.  In fact, I would be concerned if the XHTML
> spec decided to take on the burden of validating scripts and styles,
> just as I think it is out-of-scope for the spec to be placing mandates
> on the metadata that ships with a page.

I still hear a confusion between markup and content. And I may *want*
to be able to tie a CSS validator to the <style> elements and attributes,
I may want to auto-debug <script> elements. If I don't, fine. Turn off 
the feature.
 
I'm somewhat surprised to hear someone say this, as one of the biggest 
impetus for XML Schema is precisely the ability to validate content. The
battle between the "document-heads" and "data-heads" has been waging for
the past few years.

I don't think there's any danger that XHTML per se (it's specification
or its working group) would take up the burden of "validating" scripts
or styles. First off, I don't consider that validation, since validation
is limited to markup, and it's simply out of scope.

> I think I see your point about the <rdf>...</rdf> element, though -- if
> you defined such an element as (#PCDATA) it would still break as soon as
> we stuck XML with any namespaces in there.  Is that a correct assessment
> of your reluctance? 

Well, if you want to call it reluctance. It's a simple technical fact that
namespaced XML that has no DTD can't be validated according to a DTD. 
This isn't nothing special to XHTML. RDF designed by an author can't be
validated by any schema either, unless that author supplies one.

> It seems rather ironic that XHTML can happily
> validate purely random text in particular elements, but pukes as soon as
> that text becomes well-formed.  In other words, if I decided to use a
> new scripting language that was based on XML and namespaces, as soon as
> I use it in my <script /> block, the page won't validate -- XHTML: use
> anything but XML..

Again, I'm not hearing a distinction between markup and document content.
The criticism is thus unfounded.

> > is going to make validation of six or seven author-designed namespaces
> > by *any* methodology extremely difficult. XHTML modularization doesn't
> 
> This is the problem of RDF, isn't it?  In fact, the Cambridge Communiqué
> [1] seemed to conclude that XML Schema is *not* necessarily appropriate
> for RDF, and RDF is meant to be used with the RDF-Schema spec instead.

I haven't read the communiqué, but that would certainly be my assessment.
RDF is namespaces-on-steroids, so only tools designed to deal with RDF
are likely to validate RDF. But I'm actually not trying to turn this
into a diatribe against RDF. As I've said, I think specific applications
of RDF are demonstrably useful.

> > web pages will likely be quite a bit more difficult if the markup
> isn't
> > valid. In fact, a lot more difficult. I've got a small Java
> application
> 
> I think you are right about this one.
> 
> > (kinda lost track). I don't think you're going to see a stronger set
> of
> > semantic elements inside of XHTML, nor do I see a trend toward
> improving
> 
> That seems wise.
> 
> > read up on HTML and can make web pages. It'd be an order of magnitude
> > easier to get them to use <author> and <abstract> elements than to use
> > some funky namespace markup, but the direction isn't that way. Sorta
> 
> I can see what you mean here -- I am not so sure that the ultimate goal
> of RDF is to provide for a common set of semantics that everyone agrees
> upon, though. 

Agreed. I think of RDF as a very primitive toolkit, semantics-wise. One
builds something upon it.

> Dublin Core, for example, has built a lot of consensus,
> and is therefore a sort of "de-facto" metadata markup.  But this makes
> RDF (in a way) irrelevant to DC's goals (DC does more for RDF than RDF
> does for DC in the year 2001). RDF is exactly about how to do metadata
> when you *can't* get everyone to agree (which seems to be a safe
> assumption these days).  It allows people to build and evolve their own
> tools while still providing something of a bridge to the future. 

Dublin Core certainly "does more for RDF" in a sense, but only insofar
as "XHTML does more for XML than XML does for XHTML." One is simply an 
application of the other.

As I said in my last message, communication without agreeing first upon
a common language is no communication at all.  Dublin Core is enormously 
valuable precisely because of the agreements. Last I heard, WorldCat had
44 million records in it; that's a lot of agreement.

> This
> is why I compare the metadata section to the <style>...</style> block
> and point to the W3C opinion that RDF Schema is independent of XML
> Schema.  RDF is meant to be incredibly abstract and processed by
> machines that may or may not understand various pieces of the RDF.
> You're right that a messed up RDF statement could be very expensive to a
> company, but again I feel the validation of RDF statements is the
> problem of RDF and not XHTML.

If we agree we're not talking about content but markup, validation is
validation, regardless of RDF or XHTML. You use the same validation
tool even. Putting a Dublin Core module into XHTML makes good sense,
but as we seem to agree there's no possibility of an "RDF module,"
nor does one even make any sense. That'd be like having an "XML module."

Murray

...........................................................................
Murray Altheim                            <mailto:altheim&#x40;eng.sun.com>
XML Technology Center
Sun Microsystems, Inc., MS MPK17-102, 1601 Willow Rd., Menlo Park, CA 94025

      In the evening
      The rice leaves in the garden
      Rustle in the autumn wind
      That blows through my reed hut.  -- Minamoto no Tsunenobu
Received on Monday, 16 April 2001 05:12:02 GMT

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