Statements about links in XHTML 2 [was RE: customer feedback, please]

Hello Ben,

The points you raise are extremely interesting. My general feeling
though is that we have to be careful to ensure we provide generic
solutions.

First let me see if I understand the problem. You are saying that there
is some document that has a license defined externally, and you would
like to make a connection between the document and the license. In
RDF/XHTML this would be expressed as:

  <html xmlns:cc="http://web.resource.org/cc/rels/">
    <head>
      <link
       rel="cc:license"
       href="http://creativecommons.org/licenses/by-nc/1.0/"
      />
    </head>
    <body />
  </html>

Also, somewhere within the document is a link that users can navigate in
order to read the license:

> <a rel="http://web.resource.org/cc/rels/license"
> href="http://creativecommons.org/licenses/by-nc/1.0/">
> Creative Commons License
> </a>

You seem to be saying that firstly this feels like unnecessary
duplication. And secondly, it would be more correct to say that "we have
a link, and a property of this link is that it is the license for this
document".

Whilst I would sympathise - and in fact would like to solve this - I'm
very keen to do so in a generic way. It is only because you know the
'role' that @href is playing on <a> that you can decide you would like
it to express more than just being a link for users to click on. That is
difficult to generalise, though. Say the attribute was the CSS class -
what would this mean?:

  <span rel="xx:yy" class="selected"> ... </span>

Would that still be a statement about an attribute, or are we not
interested in non-URI attributes? If we can make statements about the
contents of any attribute, what would it mean if there were two
attributes on <a>? How would you decide which one you are making
statements about?

Of course, the reality is you are probably only interested in links. But
whatever solution we come up with, we wouldn't want to confine it to
just @href attributes, since there are a lot of other useful situations
where we might employ what you need. For example, XForms uses @src in
some situations:

  <xforms:model>
    <xforms:instance
     rel="xx:yy"
     src="http://example.com/intitialData"
    />
  </xforms:model>


What I'm wondering therefore, is whether we could extend the RDF/XHTML
syntax we already have; metadata can already be nested inside the items
to which it refers:

  <html xmlns:dc="http://purl.org/dc/elements/1.1/">
    <head />
    <body>
      <blockquote id="q1">
        <link rel="dc:source" resource="urn:isbn:0140449132" />
        <p>
          'Rodion Romanovitch! My dear friend! If you go on in this way
          you will go mad, I am positive! Drink, pray, if only a few
drops!'
        </p>
      </blockquote>
    </body>
  </html>

This seems to fit 'conceptually' with what you are after, although in
it's current form it doesn't work for you, for two reasons:

1. You want to make a statement about "a/@href", and not "a".
2. You want the subject of the statement to be the 'current'
   document.

The second issue looks like it needs solving anyway, and I've already
been looking into it. I'm thinking that all we need to do is retain the
use of @rev in <link>, in much the same way that it is used at the
moment. This 'reversal' syntax would be useful in many situations:

  <table id="menu">
    <link rev="widget:menu" href="#" />
    <thead />
    <tbody />
  </table>

Unfortunately, it's still not quite right for you, since this:

  <a id="lic" href="http://creativecommons.org/licenses/by-nc/1.0/">
    <link rev="cc:license" href="#" />
    Creative Commons License
  </a>

would give us this:

<> <http://web.resource.org/cc/rels/license> <#lic> .

which is close ... but not close enough!

To finish the jigsaw then, there are two ways we could go in addressing
problem 1. One is to say that:

  any URI attribute on an element can become the
  subject (or object, if using @rev) of nested
  statements.

At the moment I specifically allow the following structure:

  <link rel="dc:copyright" href="http://example.com/company/BBC/6">
    <meta property="dc:location">London</meta>
  </link>

but we could make the whole thing more general, and allow this to work
with any URI on the parent element. If we did that, we would probably
have to say that @id takes precedence though, since we still need to be
able to do this:

      <blockquote id="q1">
        <link rel="dc:source" resource="urn:isbn:0140449132" />
        <p>
          'Rodion Romanovitch! My dear friend! If you go on in this way
          you will go mad, I am positive! Drink, pray, if only a few
drops!'
        </p>
      </blockquote>

but since in XHTML 2 @href can appear anywhere, we would not want this
reference to suddenly change meaning if the author makes the quote into
a link.

The second way is to leave things as they are in RDF/XHTML (with the
addition of @rev) and work out some way of getting the information
associated with <a> out as triples too. Your syntax would then be either
this:

  <a id="lic" href="http://creativecommons.org/licenses/by-nc/1.0/">
    <link rev="cc:license" href="#" />
    Creative Commons License
  </a>

or this:

 <html xmlns:cc="http://web.resource.org/cc/rels/">
    <head>
      <link
       rel="cc:license"
       href="#lic"
      />
    </head>
    <a id="lic" href="http://creativecommons.org/licenses/by-nc/1.0/">
      Creative Commons License
    </a>
  </html>

If we could then work out a way to 'expand' all links in the document to
triples (and I have two or three ideas), then your triples would look
like this:

<> <http://web.resource.org/cc/rels/license> <#lic> .
<#lic> <http://www.w3.org/xlink/simple>
<http://creativecommons.org/licenses/by-nc/1.0/> .

(Just using XLink as a place-holder to illustrate the point.)

It would then be a simple case of adding some equivalence rules.

Before I go any further, from the metadata viewpoint is the latter
acceptable? Is the extra level of indirection a problem? Any thoughts or
preferences?

Regards,

Mark


Mark Birbeck
CEO and CTO
x-port.net Ltd.

Download our XForms processor from
http://www.formsPlayer.com/



> -----Original Message-----
> From: public-rdf-in-xhtml-tf-request@w3.org 
> [mailto:public-rdf-in-xhtml-tf-request@w3.org] On Behalf Of Ben Adida
> Sent: 19 March 2004 19:00
> To: Dan Connolly
> Cc: RDF in XHTML task force; public-swbp-wg@w3.org
> Subject: Re: customer feedback, please
> 
> 
> 
> 
> Greetings to both the TF and the WG,
> 
> 
> At Creative Commons, we need a solution for including RDF 
> statements in HTML chunks (XHTML 1.0/2.0, non-compliant HTML, 
> etc...). The two solutions presented have some attractive 
> qualities, but they don't work for CC yet.
> 
> For CC - and I believe for XHTML users in general - an RDF 
> expression solution should have the following properties:
> 	(1) a chunk of HTML, independent of the HEAD or BODY 
> tags, can include RDF statements.
> 	(2) whenever possible, RDF statements should be 
> intimately tied to what a user sees in the visible portions 
> of the XHTML.
> 
> It seems that (1) is given to us by the XHTML/RDF proposal, 
> and (2) by the GRDDL proposal, but really we need both for 
> this stuff to take off.
> 
> So, here's something that would work:
> 
> <!-- Begin Creative Commons License -->
> This document is licensed under a
> <a rel="http://web.resource.org/cc/rels/license"
> href="http://creativecommons.org/licenses/by-nc/1.0/">
> Creative Commons License
> </a>
> <!-- End Creative Commons License -->
> 
> which would be translated to N3 notation as:
> 
> <> <http://web.resource.org/cc/rels/license>
> <http://creativecommons.org/licenses/by-nc/1.0/">
> 
> Using XHTML 2, one could wrap that in a SPAN with a CC 
> namespace and have a Qname REL attribute like cc:license. Dom 
> mentioned that this is not recommended by current standards, 
> but I question why that is: isn't the end goal of this whole 
> effort to qualify links in the spirit of the web and RDF?
> 
> The really interesting aspect of this approach is that the 
> relationship is tied to what the user can observe by clicking 
> through on the link! It's just a qualification of the link, 
> which fits nicely into the RDF paradigm.
> 
> The document at the rel type URI can include all sorts of 
> additional information in RDF format, including:
> 	- a link to an XSLT script that would yield RDF/XHTML 
> (a-la GRDDL)
> 	- a human description of this type of link
> 	- links to any other tools that are relevant
> 	- etc...
> 
> Why can't we do this (or something similar)?
> 
> The GRDDL weakness is that it currently requires a HEAD 
> profile, which is bad because:
> 	- HTML chunks can't contain CC licenses
> 	- there's only one possible profile for the whole page
> 
> The XHTML/RDF weakness is that it doesn't tie the LINK to the 
> actual observable link that users click through, which leads 
> to large headaches in terms of XHTML maintenance over time 
> (say you choose a new license... are your metadata and 
> user-observable HTML link still consistent?)
> 
> How can we get these to work together to yield the highly 
> desirable properties (1) and (2) from above? In other words, 
> how can we augment the current XHTML standards to enable 
> current, "weak links" to become RDF-strong links?
> 
> -Ben
> ben@mit.edu / ben@creativecommons.org
> 
> 
> On Thu, 2004-03-18 at 11:56, Dan Connolly wrote:
> > I'd like to check in with anybody who feels like a customer, 
> > especially the intersection of this task force with the 
> Semantic Web 
> > Best Practices WG.
> 
> 
>

Received on Thursday, 25 March 2004 07:24:12 UTC