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Re: problem with blank node identifiers and rdf:nodeID

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Thu, 28 Nov 2002 16:36:24 -0500 (EST)
Message-Id: <20021128.163624.09114430.pfps@research.bell-labs.com>
To: Jan.Grant@bristol.ac.uk
Cc: bwm@hplb.hpl.hp.com, www-rdf-comments@w3.org

From: Jan Grant <Jan.Grant@bristol.ac.uk>
Subject: Re: problem with blank node identifiers and rdf:nodeID
Date: Thu, 28 Nov 2002 21:10:26 +0000 (GMT)

> On Thu, 28 Nov 2002, Peter F. Patel-Schneider wrote:
> 
> > From: Jan Grant <Jan.Grant@bristol.ac.uk>
> > Subject: Re: problem with blank node identifiers and rdf:nodeID
> > Date: Thu, 28 Nov 2002 17:32:47 +0000 (GMT)
> >
> > > To be clear: Peter's correct that there's a bug in the transformation
> > > specification in the syntax document. A "name mangler" is _not_
> > > forbidden by the specification, however, since:
> > >
> > > http://www.w3.org/TR/2002/WD-rdf-syntax-grammar-20021108/#section-Data-Model
> > >
> > > says
> > >
> > > [[
> > > This model illustrates one way to create a representation of an RDF
> > > Graph from an RDF/XML document. It does not mandate any implementation
> > > method - any other method that results in a representation of the same
> > > RDF Graph may be used.
> > > ]]
> >
> > The problem is, however, that the document does not present a way of
> > producing a unique class of equivalent RDF graphs from an RDF/XML
> > document.  For example,
> >
> > <rdf:RDF xmlns:rdf="..."
> >          xmlns:ex="...">
> >
> > <rdf:Description rdf:nodeID="n1">
> >  <ex:foo>
> >   <rdf:Description />
> >  </ex:foo>
> > </rdf:Description>
> >
> > </rdf:RDF>
> >
> > could produce either of the two following RDF graphs
> >
> > _:x1 <ex:foo> _:x1 .
> >
> > or
> >
> > _:x1 <ex:foo> _:x2 .
> >
> > which are not equivalent.
> 
> That's why the "Blank Node Identifier" generation needs documenting; and
> the use of the nodeID attribute value needs modifying when turned into a
> blank node identifier, too.
> 
> The original text predates nodeID; the doc needs a bugfix but I don't
> think it's a large one. Providing that nodeID attribute-values can't
> clash with generated ids, everything else should be ok, right?

Well, that would be a start, but there is also nothing that I can find in
the document that says that the nodeID generator needs to generate
different nodeIDs each time.  For example, the document appears to allow

<rdf:RDF xmlns:rdf="..."
         xmlns:ex="...">

<rdf:Description>
  <ex:foo>
   <rdf:Description />
  </ex:foo>
</rdf:Description>

</rdf:RDF>

to generate the following 

_:x <ex:foo> _:x .


peter
Received on Thursday, 28 November 2002 16:36:39 GMT

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