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Re: longdesc URLs and RDFa

From: Mark Birbeck <mark.birbeck@webbackplane.com>
Date: Sat, 14 Aug 2010 07:33:42 +0100
Message-ID: <AANLkTikKjC7ucN3LkqcO3Uczf4YPNM_5oHsfrHRysHG4@mail.gmail.com>
To: Leif Halvard Silli <xn--mlform-iua@xn--mlform-iua.no>
Cc: public-rdfa-wg@w3.org
Hi Leif,

This is an interesting problem.

I agree that if @longdesc has a 'meaning' in HTML 5 then there should
be a way to indicate what that meaning is so that an RDFa parser can
pick it up. I don't think it would be good to put @longdesc into RDFa
Core though, because ultimately we want to provide a framework for
host language semantics, rather than providing those semantics

So, what might work is to:

1. Add a new concept to RDFa Core that defines mappings from an
attribute name to a predicate (URI). These could be set by the host
language in just the same that terms are. This list of mappings is
then available to the parser and as traverses the tree it compares
each attribute against this list. I don't see any reason why this list
couldn't also be modified via profiles.

(We'd also need to indicate in some way whether the attribute content
is a URI or a literal, but I'm sure we can work that out.)

2. Create some template of words that could be added to a host
language specification which makes it clear to implementers that some
particular attribute requires mapping during RDFa processing.

This latter is going to be tricky given that RDFa is not actually
'present' in HTML 5. But since other metadata solutions such as
Microdata would probably also want to map @longdesc, then the host
language merely needs to mention that @longdesc maps to a predicate
with a URI of <x>, and leave it at that.

Do you think that this would capture what you want to see?


Mark Birbeck, webBackplane



webBackplane is a trading name of Backplane Ltd. (company number
05972288, registered office: 2nd Floor, 69/85 Tabernacle Street,
London, EC2A 4RR)

On Sat, Aug 14, 2010 at 3:58 AM, Leif Halvard Silli
<xn--mlform-iua@xn--mlform-iua.no> wrote:
> There is a debate in the HTMLwg about the longdesc attribute. And in
> that debate, the thought has surfaced that @longdesc,
>        <img src="*" longdesc="long.html" alt="short description" />
> is simply a *shorthand notation* for this (hypothetical) micro format
>        <a href="long.html" rel="longdesc">
>                <img src="*" alt="short description" />
>        </a>
> This has resulted in an attempt to register the 'longdesc' as link
> relation. [1] Simultaneously, a search for a better documentation of
> implementations of @longdesc has been (re)started. And in that context,
> I raised a question about RDFa and @longdesc. [2]
>        Observation 1: The XHTML+RDFa DOCTYPE supports the @longdesc
> attribute.
>        Observation 2: Mark Birbeck states in his 'Introduction to RDFa'
> article that «The @rel and @href attributes are no longer confined to
> the a and link elements, but can also be used on img to indicate a
> relationship between the image and some other item.» [3]
>        Observation 3: A longdesc link indicates a relation between a short
> description and a long description. (See the quotes from HTML4 provided
> in [1]: 'link to long description (complements alt)' and 'link to long
> description (complements title)'.)
> Questions: Would it not be logical if RDFa treated the @longdesc link
> as a semantic link - e.g. equivalent to the micro format I described
> above? What needs to be added in order to make this happen?
> [1]
> http://www.ietf.org/mail-archive/web/link-relations/current/msg00047.html
> [2] http://lists.w3.org/Archives/Public/public-html/2010Aug/0140
> [3] http://www.alistapart.com/articles/introduction-to-rdfa/
> --
> leif halvard silli
Received on Saturday, 14 August 2010 06:34:37 UTC

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