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Re: list-expansion in RDFa

From: Christoph LANGE <ch.lange@jacobs-university.de>
Date: Sat, 20 Feb 2010 13:31:24 +0100
To: Toby Inkster <tai@g5n.co.uk>
Cc: Gregg Kellogg <gregg@kellogg-assoc.com>, RDFa Community <public-rdfa@w3.org>, "public-rdfa-wg@w3.org" <public-rdfa-wg@w3.org>
Message-Id: <201002201331.34305.ch.lange@jacobs-university.de>
2010-02-20 01:19 Toby Inkster <tai@g5n.co.uk>:
> On Fri, 2010-02-19 at 15:12 -0500, Gregg Kellogg wrote:
> > However, the inability to reasonably serialize RDF lists in RDFa is a
> > shortcoming.
> 
> Serialising rdf:Lists in RDFa is ugly, ugly, ugly.

I agree that they are ugly, but sometimes you can't do without them.  Or how
_would_ one encode what Gregg meant to express?  I still think that RDF lists
are the most “standard” way of doing so.  So why not add the data structure
support known from RDF/XML to RDFa?

Or otherwise, we could give definitive recommendations on how to solve this
common problem, without always reinventing the wheel.  Two common patterns
are:

* giving every list item a numeric “index”-like property
* reinventing linked lists without using rdf:first|rdf:rest.  This has e.g.
  been done here:
  http://www.webont.org/owled/2006/acceptedLong/submission_12.pdf

A third way might be to say:  We do not _want_ to introduce (ordered) lists
into RDFa, because the order can always be derived by looking into the X(HT)ML
document that holds the RDFa annotations.  But that would be problematic
because:

* sometimes you process the RDF extracted from RDFa and no longer have access
  to the original X(HT)ML document
* encoding order directly in RDF is machine-friendlier than making reasoners
  look up order in X(HT)ML
* the fact that in XML _everything_ is ordered might give the false expression
  that non-list-like RDFa annotations also have an “ordered” semantics.

> That said, rdf:Lists have few uses outside OWL ontologies.

I would render that more precisely to “outside the RDF representation of OWL
ontologies”.  And the fact that RDF lists are internally used to represent
certain OWL constructors in RDF unfortunately makes RDF's list vocabulary
“special” for OWL reasoners, which is why one cannot use RDF lists in ABox
data that _use_ an OWL ontology.  And that's why the above-mentioned paper was
published.

Cheers,

Christoph

-- 
Christoph Lange, Jacobs Univ. Bremen, http://kwarc.info/clange, Skype duke4701

Received on Saturday, 20 February 2010 12:31:36 GMT

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