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Re: longdesc URLs and RDFa

From: Mark Birbeck <mark.birbeck@webbackplane.com>
Date: Wed, 18 Aug 2010 12:39:32 +0100
Message-ID: <AANLkTinWtG1HSCvtb7UEkJ=fsLc7NiqjFdvoK7L90_cF@mail.gmail.com>
To: Ivan Herman <ivan@w3.org>
Cc: Leif Halvard Silli <xn--mlform-iua@xn--mlform-iua.no>, Shane P McCarron <shane@aptest.com>, martin@weborganics.co.uk, W3C RDFa WG <public-rdfa-wg@w3.org>
Hi Ivan/Leif,

On Wed, Aug 18, 2010 at 11:44 AM, Ivan Herman <ivan@w3.org> wrote:
> Leif,
> thanks. I think I indeed misunderstood you. If I concentrate on the image related
> attributes, what you seem to say is that:
> - the value of @longdesc should be treated as if it was a @resource
> - the value of @alt should be treated as if it was @content
> and that is all. Correct?
> Sorry for the misunderstanding
> Ivan

This doesn't work, I'm afraid, because @longdesc, @cite and @alt are
*very* different to @resource and @content.

@resource and @content are generic containers for objects (and
subjects...sometimes) and for that reason are general-purpose. We
added support for @src for the same reason -- that it's generic.

@alt, @cite and @longdesc on the other hand are predicate/object
couplets, and for that reason they require a decision to be made about
which predicate to map to. If we were to do that mapping then it would
take us away from providing a generic *framework* for semantics, to
actually defining the semantics themselves.

That's why at the very beginning of this discussion I said that we
should look at how we allow host languages to define their own
'mappings' from attributes and elements to predicates. If we provided
that capability it would then allow people to define an interpretation
not only for @alt, @cite and @longdesc, but also for <title> and a
bunch of other things, too.

(<title> is a good example of the problem we face once we move into
semantics; should <title> map to 'dc:title'? Lots of people think it
should, and we could spend weeks just discussing that. My response
would be that it's none of our business -- we are in the business of
providing a *framework* for semantics, and we let other people define
the semantics themselves.)

The only attribute we have in the current spec that is comparable to
@cite et.al, is @typeof, which represents *both* a predicate of
'rdf:type' *and* a resource. However, that particular exception is
driven by the needs of RDF and not HTML.

So in summary, I don't doubt that it's possible to come up with
suitable mappings for these attributes, but I don't believe it's our
place to do so. A fundamental tenet of RDFa from the start was to
focus on a framework for semantics rather than the semantics
themselves, and that is what allowed us to avoid the 'Microformats
trap' (i.e., leave the definition of any actual semantics to the



Mark Birbeck, webBackplane



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Received on Wednesday, 18 August 2010 11:40:27 UTC

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