W3C home > Mailing lists > Public > www-rdf-interest@w3.org > March 2001

Again: Anonymous Resources

From: Stefan Kokkelink <skokkeli@mathematik.uni-osnabrueck.de>
Date: Thu, 08 Mar 2001 12:26:38 +0100
Message-ID: <3AA76C6E.67D74442@mathematik.uni-osnabrueck.de>
To: Aaron Swartz <aswartz@swartzfam.com>
CC: RDF interest group <www-rdf-interest@w3.org>
Hi Aaron,

moving this to RDF-IG, might me interesting for the
group ...

Aaron:

> >Umm. All resources have URIs -- that's their definition, I believe.

Stefan:

> > No: every resource *can* have a URI. In my opinion it would be a hard
> > restriction to RDF if one could only decribe resources that have a name ...
> > There are many things in the world that don't have names.

Aaron:

> Perhaps, but the act of describing them gives them a name. i.e. the first
> thing you described in file://C:\Test\RDF\q.rdf would usually be known as
> file://C:\Test\RDF\q.rdf#genid1 -- how does CARA deal with this? SiRPAC and
> other programs I've used make up URIs like the one above for anonymous
> nodes.

Yes, but this raises some problems. For example try the
following code in SiRPAC [1]:

<?xml version="1.0"?>
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
         xmlns:dc="http://purl.org/dc/elements/1.1/">
  <rdf:Description>
    <dc:type>animal</dc:type> 
  </rdf:Description>
  <rdf:Description about="online:#genid1">
    <dc:type>no, only an anonymous resource</dc:type> 
  </rdf:Description>
</rdf:RDF>

I don't think this is a specific problem in SiRPAC. You always have
this problem when trying to calculate a URI for an anonymous 
resource.

(Note: If you use CARA [2] you should use the GraphViz visualization to
look at the RDF graph. The (default) triple representation is 
broken!)

If we really want that anonymous resources are given URIs by parsers
we need to define a special URI scheme for these (no longer ;-)
'anonymous' resources and a well-defined algorithm how parsers
should calculate these URIs from the XML serialization. 

(But this is not easy: we would have to ensure that anonymous resources
from
different RDF files get *different* URIs!. Otherwise it becomes almost
impossible to join RDF graphs in a meaningful way. One advantage of 
anonymous resources is that they are not glued with other resources
when joining graphs!)

Currently, we don't have such a scheme defined
in the RDF specification nor an algorithm to calculate 
these URIs. 

Perhaps RDFCore should try to clarify things.

Personally I think it is a bad idea to require everything we want
to decribe with RDF to have a name. (Humans don't do this: we often
decribe things by the properties they have.) That would raise a lot
of problems ...


Greetings,
Stefan

[1] http://www.w3.org/RDF/Implementations/SiRPAC/
[2] http://zoe.mathematik.Uni-Osnabrueck.DE/RDF/parser.html
Received on Thursday, 8 March 2001 06:27:02 GMT

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