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Re: Display values for RDFa object URLs

From: Manu Sporny <msporny@digitalbazaar.com>
Date: Fri, 10 Aug 2007 10:19:32 -0400
Message-ID: <46BC73F4.60204@digitalbazaar.com>
To: RDFa mailing list <public-rdf-in-xhtml-tf@w3.org>

This "display values for URLs" and "automatically generating triples"
discussion is one that's been going on in the Microformats community for
several months (if not years) [1][2][3].


+1: We don't want to guess at what the publishers intent is...

Here's a real-world problem that we've hit with hAudio uF:

   <div about="#song" instanceof="hmedia:Audio">
    <a rel="hmedia:sample"
          <img src="images/sample.png" alt="Image of Sample" />
          A Sample

Do you use the text "Image of Sample", or "Sample" in this case? How
deeply to you peek into sub-elements? The Microformats community is
still deliberating on this. Most have identified this as an parser
implementation detail that the parser authors need to deal with. It
looks like the community is not going to take a stance on it :).

My take is that we need to publish a "best practices" to guide for the
hAudio parser writers and let them know what a reasonable display value
fallback should be:

1. If @title is given for the A element, use that.
2. Use the text that would be shown for the link text if there are no
   other markup elements in the link text (such as an image).
3. If there is an image with @alt specified, use the value that would be
   displayed in a text-browser or screen reader.

and so on...

However, the RDFa folks don't need to take this approach as there seems
to be a better option (using rdfs:label explicitly).


+1: for explicitly stating what you want an rdfs:label to be.

   <div about="#song" instanceof="hmedia:Audio">
    <a rel="hmedia:sample"
          <img property="rdfs:label" src="images/sample.png"
               alt="Image of Sample" />
          A Sample

In the above example, the publisher has made it explicit that they want
"Image of Sample" to be the rdfs:label for the @href. I don't think it
is too much to ask publishers to specify an rdfs:label if they have a
preference. If they don't have a preference, then it would be up to the
application to pick something. I don't think this is a decision that the
RDFa folks should be making for the application authors. In other words:
we should enable people to specify display values, but we shouldn't try
to guess what those values should be. Keep RDFa lean and put the power
to explicitly state display values in the publishers hands. :)


In general, metadata markup such as this should be explicit, not
implicit. The publisher should be able to explicitly state what the
value should be... if they don't have a preference, that decision should
be left up to the application author. This approach means that:

- We don't have to change/complicate the parsers.
- The publisher has full control on the RDFa output.
- This "rdfs:label concept" should probably be placed in a "best
  practices" document.

Just my $0.02...

-- manu


Manu Sporny
President/CEO - Digital Bazaar, Inc.
DB Blog: Bitmunk Blazes Path in Film and TV
Received on Friday, 10 August 2007 14:19:41 UTC

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