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Re: longdesc URLs and RDFa

From: Ivan Herman <ivan@w3.org>
Date: Sat, 14 Aug 2010 16:28:41 +0200
Cc: public-rdfa-wg@w3.org
Message-Id: <E67960B3-7E84-40B1-9F4B-5F0597756019@w3.org>
To: Leif Halvard Silli <xn--mlform-iua@xn--mlform-iua.no>
Hi Leif,


On Aug 14, 2010, at 14:01 , Leif Halvard Silli wrote:
[snip]
> 
>> Note that registering the longdesc (and alt) as 'terms' as we call 
>> them in RDFa, ie, as specific and predefined property/rel types, is 
>> much easier to do and we are in the process of defining the mechanism 
>> and the content to do that for HTML or XHTML. Ie, that can be done 
>> easily, and no matter what. But what this means is that the users 
>> would have to manually write the <img> elements the way I wrote them 
>> up there. 
> 
> The IMG element you presented above was lacking both the longdesc 
> attribute (you replaced it with a resource attribute). And it also 
> lacked the alt attribute (you replaced it with a content attribute). 
> Perhaps you could show a complete example with BOTH the @longdesc and 
> @alt attributes in addition to the RDFa attributes that are necessary?
> 

I am not sure I understand the question. What I tried to say is that if the original HTML code contains

<img src="*" longdesc="long.html" alt="short description" />

then this could be replaced, conceptually or by some sort of a preprocessor, by

<img src="i.src" rel="longdesc" resource="long.html" property="alt" 
content="short description" />

which is a perfectly o.k. RDFa 1.1 code with the proviso that the 'longdesc' and 'alt' terms are predefined for (X)HTML+RDFA as 'http://someuriforlongdesc' and 'http://someuriforalt', respectively (if those are not predefined, then @rel and @property should the full respective URI as values). Which means that, again conceptually, both longdesc and alt could be replaced in the HTML by these, but the authors have to do something else than today.

This is of course conceptual and techie. Mainly for the @alt attribute the complete removal from the language would (rightfully!) raise lots of eyebrows in the accessibility community, so I am doubtful that would be a really good idea. But that is a different discussion... I just wanted to make the technical point clearer.

I hope I made myself more clear. Sorry for the possible confusion.

Ian 





> Leif
> 
> 
>> Cheers
>> 
>> Ivan
>> 
>> 
>> On Aug 14, 2010, at 04:58 , Leif Halvard Silli 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
>>> 
>> 
>> 
>> ----
>> Ivan Herman, W3C Semantic Web Activity Lead
>> Home: http://www.w3.org/People/Ivan/
>> mobile: +31-641044153
>> PGP Key: http://www.ivan-herman.net/pgpkey.html
>> FOAF: http://www.ivan-herman.net/foaf.rdf
>> 
>> 
>> 
>> 
>> 


----
Ivan Herman, W3C Semantic Web Activity Lead
Home: http://www.w3.org/People/Ivan/
mobile: +31-641044153
PGP Key: http://www.ivan-herman.net/pgpkey.html
FOAF: http://www.ivan-herman.net/foaf.rdf







Received on Saturday, 14 August 2010 14:27:18 GMT

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