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Re: Bug in RDF Distiller

From: Gregg Kellogg <gregg@kellogg-assoc.com>
Date: Mon, 22 Aug 2011 15:29:23 -0400
To: Jeni Tennison <jeni@jenitennison.com>
CC: W3C RDFWA WG <public-rdfa-wg@w3.org>
Message-ID: <C74F2FB6-8593-4AF8-B7C4-B9D4E13EAA3D@greggkellogg.net>
I'm CCing the RDFa WG, as this suggests a possible issue with precedence of terms from the default profile and @vocab, which I believe has been discussed before.

> Hi Gregg,
> 
> I'm trying out mapping some microdata examples into RDFa, and came up with this RDFa to represent a list:
> 
>    <div vocab="#" typeof>
>     <p>Flavors in my favorite ice cream:</p>
>     <div rel="flavor">
>      <ul vocab="http://www.w3.org/1999/02/22-rdf-syntax-ns#" typeof="List">
>       <li property="first">Lemon sorbet</li>
>       <li rel="rest">
>        <span typeof="List">
>         <span property="first">Apricot sorbet</span>
>         <span rel="rest" resource="nil"></span>
>        </span>
>       </li>
>      </ul>
>     </div>
>    </div>
> 
> aiming to get:
> 
>    @prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
>    [] 
>      <#flavor> [
>        a rdf:List ;
>        rdf:first "Lemon sorbet" ;
>        rdf:rest [
>          rdf:first "Apricot sorbet" ;
>          rdf:rest rdf:nil ;
>        ] ;
>      ] ;
>      .
> 
> What I actually get with your RDF Distiller is:
> 
> @prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
> 
> <> <#flavor> [ a rdf:List],
>   [ <#rest> [ <#first> "Apricot sorbet";
>       <#rest> <nil>;
>       a <#List>]] .

As previously mentioned, there is a special rule on the root element (and <head> and <body> with HTML+RDFa) in which @about="" is assumed, so this will not generate a BNode as the top subject.

It's not parsing @resource="nil" as a vocab-expanded URI, but as a document-relative URI. This is because the rules for @resource don't include terms, and @vocab uses the same rules as term (SafeCURIEorCURIEorURI not TERMorCURIEorAbsURI). To make this work, you'll need to use a full URI or a CURIE. Using @resource="rdf:nil" should work, as the 'rdf' prefix is defined in the default profile.

One more gotcha I discovered: If you process the document as HTML+RDFa, @property="first" doesn't generate rdf:first, as the @vocab might indicate; rather, it generate xhv:first; this is because the (X)HTML+RDFa spec defines "first" as a term in the default profile, which trumps @vocab. So, really, your example can only work reliably if you use rdf: prefixes throughout. It worked in the distiller, as it wasn't identified as being an HTML document.

   <div vocab="#" typeof>
    <p>Flavors in my favorite ice cream:</p>
    <div rel="flavor">
     <u typeof="rdf:List">
      <li property="rdf:first">Lemon sorbet</li>
      <li rel="rdf:rest">
       <span typeof="rdf:List">
        <span property="rdf:first">Apricot sorbet</span>
        <span rel="rdf:rest" resource="rdf:nil"></span>
       </span>
      </li>
     </ul>
    </div>
   </div>

Would you assume that @vocab should trump terms in the default profile (now renamed to something else, due to dropping @profile)? If so, please file a bug.

Gregg

On Aug 14, 2011, at 3:16 PM, Jeni Tennison wrote:

> ...
> Cheers,
> 
> Jeni
> -- 
> Jeni Tennison
> http://www.jenitennison.com
> 
Received on Monday, 22 August 2011 19:31:16 UTC

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