W3C home > Mailing lists > Public > semantic-web@w3.org > December 2007

Re: RDF/XML and named graphs

From: Jeremy Carroll <jjc@hpl.hp.com>
Date: Wed, 19 Dec 2007 15:05:19 +0000
Message-ID: <4769332F.3030600@hpl.hp.com>
To: Richard Cyganiak <richard@cyganiak.de>
CC: Chris Richard <chris.richard@gmail.com>, Steffen Staab <staab@uni-koblenz.de>, Peter Ansell <ansell.peter@gmail.com>, Fabien Gandon <Fabien.Gandon@sophia.inria.fr>, p.roe@qut.edu.au, j.hogan@qut.edu.au, Semantic Web <semantic-web@w3.org>

Richard Cyganiak wrote:
> In every other regard, RDF/XML is a complete and utter train wreck. 
> Adding named graph support to RDF/XML would be polishing a turd.
> 

I used to think this, but have been slowly coming round to seeing some 
of the advantages of RDF/XML ....

To engage in self quotation, from:

http://www.hpl.hp.com/techreports/2004/HPL-2004-56.pdf
(Carroll + Stickler, p6)

What's Right With RDF/XML?

Given the number of suggestions for change and RDF/XML's lack of 
popularity with the practioners, why does it continue?
Once you get used to it, it is surprisingly concise. The RDF data model, 
in which everything is triples, is inevitable verbose - but writing 
these triples in RDF/XML tends to ameliorate things.

The use of qnames to abbreviate URI references is concise, and 
sufficiently liked that this convention is widely used, also in non-XML 
contexts, e.g. in N3 [N3], and the OWL Semantics [OWL S&AS] document. 
The use of typed nodes, to avoid making a common triple explicit, adds 
to the efficiency with which RDF/XML encodes the RDF graph, and permits 
syntaxes which, to some extent, hide the underlying triple structure.

This hiding of the triple structure makes it easy for users to get into 
an RDF application such as OWL with only a partial understanding of its 
representation in RDF.
However, RDF/XML neithers permits complete hiding of the underlying RDF, 
nor does it make it clear what that underlying RDF is. We suggest that 
it is better to have clarity in the basic syntax, with hiding achieved 
by using alternative syntactic forms that are transformed into the basic 
syntax.
RDF/XML also provides a number of syntactic features which are useful 
for certain sorts of construct:
  rdf:parseType="Literal" is the only sensible way of embedding XML 
into the RDF graph. (The alternative requires knowledge of Exclusive XML
Canonicalization [Excl XML C14N]).
  rdf:parseType="Collection" is useful when writing OWL Ontologies [OWL
Ref].
  rdf:parseType="Resource" is used extensively in XMP [XMP].
  The use of property attributes is useful when embedding RDF in HTML.

Thus many communities find that while RDF/XML has many features they do 
not like, certain key features are highly attractive and keep them enagaged.


=====

If you want concise compact XML (if that isn't a contradiction), with 
the extensibility of RDF, then actually working from, rather than 
against RDF/XML is not an appalling idea.

Jeremy
Received on Wednesday, 19 December 2007 15:06:00 GMT

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