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Re: POWDER-related questions about RDFa linkage

From: Ivan Herman <ivan@w3.org>
Date: Sun, 04 Nov 2007 09:49:44 +0100
Message-ID: <472D87A8.8020700@w3.org>
To: "Hausenblas, Michael" <michael.hausenblas@joanneum.at>
CC: Phil Archer <parcher@icra.org>, public-powderwg@w3.org, RDFa <public-rdf-in-xhtml-tf@w3.org>
:-)

Ivan

Hausenblas, Michael wrote:
> Kudos to Ivan, who knew that I was on travel and unfortunately
> not able to respond earlier. I myself could certainly not have
> done it better ;)
> 
> Cheers,
> 	Michael
> 
> ----------------------------------------------------------
>  Michael Hausenblas, MSc.
>  Institute of Information Systems & Information Management
>  JOANNEUM RESEARCH Forschungsgesellschaft mbH
>  Steyrergasse 17, A-8010 Graz, AUSTRIA
> ---------------------------------------------------------- 
> 
>> -----Original Message-----
>> From: Ivan Herman [mailto:ivan@w3.org] 
>> Sent: Thursday, November 01, 2007 1:11 PM
>> To: Phil Archer
>> Cc: Hausenblas, Michael; public-powderwg@w3.org; RDFa
>> Subject: Re: POWDER-related questions about RDFa linkage
>>
>> If you allow me to impersonate Michael for the moment:-) 
>> (which does not mean that he cannot answer!:-)
>>
>> Phil Archer wrote:
>>> Michael,
>>>
>>> As you and others have been kind enough to look at the 
>> potential usage 
>>> of RDFa and POWDER, I'd like to ask a couple of questions please.
>>>
>>> I'd like to significantly improve what we say about RDFa, either in 
>>> the Rec Track Description Resources doc [1] or, if more 
>> appropriate, 
>>> in a non-normative POWDER Primer we'll be starting work on 
>> later this month.
>>> Easier question first. Can I ask you for a sanity check on this 
>>> example
>>> please:
>>>
>>> Example 1
>>> =========
>>>
>>> <html
>>>   xmlns="http://www.w3.org/1999/xhtml"
>>>   xmlns:wdr="http://www.w3.org/2007/05/powder#"
>>>   <head>
>>>     <title>The English Civil War</title>
>>>     <link rel="wdr:describedBy"
>>> href="http://education.example.org/powder.rdf#DR_1" />
>>>   </head>
>>>   <body>
>>>     ...
>>>     <p>Charles I came to the throne believing in his Divine 
>> Right to 
>>> rule...
>>>     ...
>>>   </body>
>>> </html>
>> Although we do not have it in the current document yet, we 
>> will have an RDFa profile, too. It may not be mandatory to 
>> use it, but advised. Ie, you should probably add the
>>
>> <head profile="http://www.w3.org/ns/rdfa/">
>>   ....
>>
>> Otherwise, this should be o.k.; it will generate the triple
>>
>> <URI-of-the-document> wdr:describedBy
>> http://education.example.org/powder.rdf#DR_1.
>>
>>> That is, a single use of wdr:describedBy at document level. 
>> Actually, 
>>> for this kind of linkage from an HTML doc, the usual way will be to 
>>> use an HTML profile we're drafting and a relationship type 
>> of powder thus:
>>> Example 2
>>> =========
>>>
>>> <html xmlns="http://www.w3.org/1999/xhtml">
>>>    <head profile="http://www.w3.org/2007/10/powder-profile">
>>>       <link rel="powder"
>>>          href="http://education.example.org/powder.rdf#DR_1" />
>>>       <title>The English Civil War</title>
>>>    </head>
>>>    <body>
>>>       <p>Charles I came to the throne believing in his 
>> Divine Right to 
>>> rule...</p>
>>>    </body>
>>> </html>
>>>
>> Actually... this is still in flux. At the moment, the RDFa 
>> rule is that @rel values without a prefix will be ignored. We 
>> do not have (yet?) a general mechanism that would allow an 
>> RDFa processor to understand a profile in the head 
>> automatically and take those @rel values. Ie, it may be 
>> better to stick with the wdr: prefix. (As I said: this is 
>> still a bit in flux, the TF members may well chime in here!)
>>
>>> But I'm really hoping that RDFa can be used for more 
>> powerful things. 
>>> In particular, that we can use it to link to a Description Resource 
>>> that describes the target of a hyperlink as simply as 
>> possible. If I 
>>> understand RDFa correctly that means doing something like this:
>>>
>>> Example 3
>>> =========
>>>
>>> <html
>>>   xmlns="http://www.w3.org/1999/xhtml"
>>>   xmlns:wdr="http://www.w3.org/2007/05/powder#"
>>>   <head>
>>>     <title>The English Civil War</title>
>>>     <link rel="wdr:describedBy"
>>> href="http://education.example.org/powder.rdf#DR_1" />
>>>   </head>
>>>   <body>
>>>     ...
>>>     <p>Charles I came to the throne believing in his
>>>     <link about="#divRight" rel="wdr:describedBy"
>>>          href="http://education.example.org/powder.rdf#DR_2">
>>>     <a href="http://education.example.org/divine_right.html"
>>>          id="divRight">Divine Right</a> to rule...
>>>     ...
>>>   </body>
>>> </html>
>>>
>> First of all: RDFa does not change the content model of 
>> XHTML1, ie, the <link> element is _not_ permitted in the body.
>>
>>
>> <html
>>    xmlns="http://www.w3.org/1999/xhtml"
>>    xmlns:wdr="http://www.w3.org/2007/05/powder#"
>>    <head profile="http://www.w3.org/ns/rdfa/">
>>      <title>The English Civil War</title>
>>      <link rel="wdr:describedBy"
>> href="http://education.example.org/powder.rdf#DR_1" />
>>    </head>
>>    <body>
>>      ...
>>      <p>Charls I came to the throne believing in his
>>      <a
>>        about="http://education.example.org/powder.rdf#DR_2"
>>        rev="wdr:describedBy"
>>        href="http://education.example.org/divine_right.html">Divine
>> Right</a> to rule...
>>
>>      ...
>>    </body>
>> </html>
>>
>> The trick is the usage of @rev and not @rel; @rev, 
>> essentially reverts the roles for subject and object. I guess 
>> this is what you want, right?
>>
>> I hope this helps.
>>
>> Ivan
>>
>>
>>
>>
>>> So we have a hyperlink in the document to one about divine 
>> right. That 
>>> second document is the subject of a triple thus:
>>>
>>> <http://education.example.org/divine_right.html>
>>>   wdr:describedBy
>>> <http://education.example.org/powder.rdf#DR_2>
>>>
>>> is there a more terse way of creating this triple within 
>> the RDFa/XHTML?
>>> I guess the problem is that would entail having two href 
>> attributes in 
>>> a single hyperlink, which is silly, but the use cases are 
>> pretty clear 
>>> for us. For example, imagine that the English Civil War document is 
>>> mobileOK and is being displayed on a mobile device - should 
>> my browser 
>>> display the hyperlink to the divine right document or not? If it's 
>>> mobileOK too (as declared in DR_2) then the answer's yes, 
>> if not, then 
>>> just show the text without the hyperlink.
>>>
>>> Finally, how far can we go in a Rec Track document that 
>> we're hoping 
>>> to declare as at Last Call after next week's face to face? 
>> Is Example 
>>> 1 sound? Is Example 3 sound?
>>>
>>> Thanks very much for your help,
>>>
>>> Phil.
>>>
>>> [1] http://www.w3.org/TR/2007/WD-powder-dr-20070925/#semlink
>>>
>> -- 
>>
>> Ivan Herman, W3C Semantic Web Activity Lead
>> Home: http://www.w3.org/People/Ivan/
>> 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/
PGP Key: http://www.ivan-herman.net/pgpkey.html
FOAF: http://www.ivan-herman.net/foaf.rdf

Received on Sunday, 4 November 2007 08:49:59 GMT

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