RE: POWDER-related questions about RDFa linkage

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
> 
>

Received on Saturday, 3 November 2007 20:32:21 UTC