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Re: Comments on RDFa in XHTML Syntax draft

From: Mark Birbeck <mark.birbeck@x-port.net>
Date: Mon, 24 Mar 2008 14:34:47 +0000
Message-ID: <a707f8300803240734t4e1222d5s8631af1b0308880c@mail.gmail.com>
To: "Laurens Holst" <lholst@students.cs.uu.nl>
Cc: public-rdf-in-xhtml-tf@w3.org

Hi Laurens,

>  I have two comments on the current RDFa in XHTML Syntax draft [1]:
>
>  First of all, I think the @cite attribute on blockquote and q elements
>  should have the same status as @href (be considered as @resource), so
>  that RDFa can pick up on existing cite attribute annotations in
>  documents, and to avoid authors having to write the citation URI twice,
>  one for RDFa and one for HTML. See the example in section 6.3.2.1.

Speaking for myself, I absolutely agree. :) However, I have never
pushed this in the current version of RDFa, because in some research
that I did for the IPTC a while ago, it looked like you could create a
general rule where:

  any attribute + value

is equivalent to:

 bnode + predicate based on attribute name + value

You'll see that @instanceof follows this pattern:

  @instanceof="t"

=>

  _:a rdf:type <t> .

A similar example would be @role:

  @role="r"

  _:a xhv:role <r> .

And I think @cite should behave the same way, since it is the citation
of a quote:

  <blockquote
   property="ab:cd"
   cite="http://www.example.org/source"
  >
    Some text.
  </blockquote>

Would give:

  _:a ab:cd "Some text." .
  _:a xhv:cite <http://www.example.org/source> .

Where ab:cd was some appropriate predicate for a quote.

However...

I'm explaining all of this, only to show that there would be much to
discuss in resolving this issue. And I think it would be too much to
hope to use @cite in a way that everyone would agree on, in this
version of RDFa. My suggestion would be to leave this until the next
version.


>  Second, are you sure that it is a good idea to give @src different
>  semantics than @href? I think it would probably be better if they had
>  the same semantics in RDFa. The reason for this is that I find the
>  difference between overriding @src and @href values (as explained in the
>  Primer [2] section 3.6) confusing, and it is not really clear to me why
>  they are treated differently. After all, they both reference a resource
>  in a very similar manner, only differing in the way the resource is
>  displayed.
>
>  The usefulness of treating @src as @about also seems to be rather
>  limited, as <img> can not have child content and you can thus specify at
>  most three triples; one with a literal object, one with a resource
>  object, and one reverse relation of the resource. Or, maybe @href should
>  also be treated as @about?

You are right that there is not a great deal of difference between
using @src as a subject or an object in the presence of @rel. However,
by making @src act as a subject, you are able to make use of an image
in some statement, and then say something about the image.

For example, you could say that someone has a picture, and that the
picture is licensed under some CC license:

  <div about="#me">
    <span property="foaf:name">Mark Birbeck</span>
    <span rel="foaf:depiction">
      <img src="pic.png" rel="license" resource="http://cc..."/ >
    </span>
  </div>

If you let @src play the role of an object, then you'll see that you
can only make one or other of these statements in a compact way, and
then you have to repeat the URI for the image, in order to indicate
the second statement. For example:

  <link about="pic.png" rel="license" href="http://cc..." />

  <div about="#me">
    <span property="foaf:name">Mark Birbeck</span>
    <img rel="foaf:depiction" src="pic.png" />
  </div>

(This is not an official response from the group, I'm merely letting
you know the thinking that lay behind this.)


>  I hope these comments (although a few days late for the comments
>  deadline, I understand) will be useful for you to improve the specification.

They have been useful, thank-you.

Regards,

Mark

-- 
  Mark Birbeck

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Received on Monday, 24 March 2008 14:35:24 UTC

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