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RE: RDF [was: Proposed changes]

From: Libby Miller <Libby.Miller@bristol.ac.uk>
Date: Sun, 26 Oct 2003 10:57:08 +0000 (GMT)
To: Danny Ayers <danny666@virgilio.it>
Cc: atom-syntax <atom-syntax@imc.org>, Www-Rdf-Interest <www-rdf-interest@w3.org>
Message-ID: <Pine.GSO.4.58.0310261036290.14938@mail.ilrt.bris.ac.uk>


I've not been following all the detail of this thread, but I am
interested in the general area, and I'd like to clear up one thing which
seems small but pertains to Danny's good point about mapping the
relationship between the RDF and XML model requiring precoordination.

(I hope this is useful - it's difficult to know how to commmunicate
between these two communities effectively. I'm an RDFista* interested
in query, calendaring, blogging among other things.)

There is no real distinction between metadata and data. The association
of RDF and the term 'metadata' seems to be something to do with intial
uses of RDF for Dublin Core (data about documents). RDF is just data;
and RDF makes somewhat explicit an underlying model of objects and
their relationships which is usually present in data-orientated XML but
- as danny says - implicitly. What this means is you have to
precoordinate with someone who has built XML data or an XML schema -
you have to extract the information from their brain somehow, not just
from the document.

RDF takes you a little way towards not requiring this precoordination,
because it is about objects and their relationships, and which is
information extractable by machines from the syntax (however poorly
the syntax expresses this to a human). This and RDF schema and OWL can
help distribute the burden of vocabulary creation while enabling
some interoperability.


* http://www.tbray.org/ongoing/When/200x/2003/10/07/Bristol

On Sun, 26 Oct 2003, Danny Ayers wrote:

> > > A potentially cool bit is that I think it should be possible to
> > do this on
> > > the fly : an RDF query could ask for all links in the content
> > of that entry,
> > > and the RDF store could get as far as <content> but then an XPath query
> > > could be carried out on that, the results expressed in the RDF model.
> >
> > How would that work?  It seems to me that if you solve that, you have
> > essentially eliminated the need for a special RDF/XML syntax - i.e., any
> > XML could be directly consumed by an RDF application.
> This is essentially along the lines of Uche's statement [1] "There is no
> syntax" -
> [[
> The trick is to extract key metadata from XML documents -- or even
> non-markup formats such as RDBMS -- and synchronize it into RDF models. You
> can then treat these as a localized semantic Web.
> ]]
> This only works when you have prior knowledge of the XML format. If you have
> have that, you can usually make a direct mapping between that XML and the
> RDF model. The weak link is when you start mixing stuff up from different
> namespaces - the mapping might no longer hold, and you'd have to define it
> not only for every language, but for every combination of languages. Using
> RDF/XML ensures there's always a mapping to the RDF model.
> > > Why not do it all as XML/XPath? Main reason being that the XML tree
> > > structure doesn't match the web's general directed graph
> > structure, probably
> > > a more immediate practical problem being that the subtrees aren't very
> > > portable across systems (merging isn't straightforward).
> >
> > It seems to me that the web's general structure is one where links tend
> > to be embedded in mixed content.
> Looking up from the source, yes, but from a few 1,000 feet it looks like
> objects (documents) that are linked together.
> > > some related notes : http://dannyayers.com/archives/001981.html
> >
> > Case in point: the above is an XML document with a number of links to
> > your own site, and one to Simon Willison's site.
> Right, and there is a disconnect between the semantics within the content
> and any explicit semantics expressed outside. For the (RDF) Semantic Web the
> links are latent semantics. As well as the need to get the 'blatant'
> metadata systems sorted out (RDF storage, RDF/OWL inference etc), I
> personally believe it's necessary to bridge to the latent semantics -
> metadata hidden in XML and things like text search (Bayesian categorizing
> etc, to infinity and beyond...). The blatant metadata systems are in the
> (early) implementation phase, but the bridging to latent metadata still
> hasn't been covered systematically. Fortunately I reckon most of the
> groundwork has already been done (e.g. XPath), so it's only matter of gluing
> the pieces together.
> Cheers,
> Danny.
> [1] http://www-106.ibm.com/developerworks/xml/library/x-think12.html
Received on Sunday, 26 October 2003 05:59:29 UTC

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