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Re: N-Triples: Naming anonnodes

From: Graham Klyne <Graham.Klyne@Baltimore.com>
Date: Mon, 23 Jul 2001 21:15:52 +0100
Message-Id: <5.1.0.14.2.20010723211223.03c4c0c0@joy.songbird.com>
To: Brian McBride <bwm@hplb.hpl.hp.com>
Cc: Aaron Swartz <me@aaronsw.com>, w3c-rdfcore-wg@w3.org
At 11:44 AM 7/22/01 +0100, Brian McBride wrote:


>Aaron Swartz wrote:
>[...]
> > Today I came up with the idea that we could define anonymous
> > nodes as having a special representation in the abstract syntax,
> > but define the N-Triples conversion from RDF as having a
> > well-defined set of names for them. IOW, an algorithm such as
> > the one used by SiRPAC or CARA to generate anonymous nodes in
> > order could be specified somehow (using XSLT, for example), and
> > all RDF/XML parsers which outputted N-Triples could follow this
> > specification. That way, comparison of N-Triples documents could
> > be reduced to a simple sort/diff operation, while still
> > retaining the semantics of anonymous nodes.
> >
> > An example:
> > <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
> > <rdf:Description>
> >    <rdf:value>foo</rdf:value>
> > </rdf:Description>
> > </rdf:RDF>
> >
> > could be unambiguously defined as:
> >
> > _:g0 rdf:value "foo" .
> >
> > as parsers would use anonymous node names in the form of _:gn
> > where n begins at zero and increments for each anonymous node
> > reached in the XML.
> >
> > Obviously this wouldn't work for N-Triples output from a data in
> > which ordering information had been lost (I have some ideas on
> > that one too, but they are less formed) but it would work for
> > any RDF/XML -> N-Triples conversion.
>
>Nice idea.  Basically this would allow easy compare of models that
>came from the same RDF/XML serialization.
>
>One thing it wouldn't handle is the following example:
>
>  <rdf:Description>
>   <foo:bar>foobar</foo:bar>
>  </rdf:Description>
>  <rdf:Description>
>   <bar:foo>barfoo</bar:foo>
>  </rdf:Description>
>
>compared to:
>
>  <rdf:Description>
>   <bar:foo>barfoo</bar:foo>
>  </rdf:Description>
>  <rdf:Description>
>   <foo:bar>foobar</foo:bar>
>  </rdf:Description>
>
>These are representations of equivalent graphs which graph compare
>will find equivalent.

Brian,

I don't think it's a reasonable goal that a (simple) parser will generate 
identical N-triples for equivalent graphs.  I think it's enough that the 
structures generated do not impede the design/application of an algorithm 
to determine graph equivalence.

[...]
>If so, we are back into the complexities of graph theory.

I don't think we ever seriously got away from them if we want to evaluate 
graph-equivalence.

#g


------------------------------------------------------------
Graham Klyne                    Baltimore Technologies
Strategic Research              Content Security Group
<Graham.Klyne@Baltimore.com>    <http://www.mimesweeper.com>
                                 <http://www.baltimore.com>
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Received on Monday, 23 July 2001 18:06:02 EDT

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