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Re: #rdfms-identity-anon-resources: provenance

From: pat hayes <phayes@ai.uwf.edu>
Date: Mon, 23 Jul 2001 22:27:16 -0700
Message-Id: <v04210122b782b575e617@[]>
To: Brian McBride <bwm@hplb.hpl.hp.com>
Cc: w3c-rdfcore-wg@w3.org
>I was chatting with a colleague to day and the subject of anon resources
>and provenance came up.
>Assume I recieve the following rdf from some source SOURCE, possibly with a
>digital signature:
>  <rdf:Description>
>    <foo:bar>foobar</foo:bar>
>  </rdf:Description>
>  <rdf:Description rdf:about="http://goo">
>    <foo:bar><foobar</foo:bar>
>  </rdf:Description>
>If were to represent this in my machine as:
>  <gensym:1234> <foo:bar> "foobar" .
>  <http://goo>  <foo:bar> "foobar" .
>this is not the information that SOURCE signed - SOURCE made no assertion
>about <gensym:1234>.  We'd have to be able to distinguish between the
>gensym'd URI and the 'real' one.

As I said a while ago, it matters who generates the gensym. If SOURCE 
uses an anonymous node (existential quantifier) then indeed you are 
not entitled to replace it with a gensym and say that it represents 
what SOURCE said. That is what the logic says also: the step from the 
existential to the skolem form is *not* a valid inference, so you 
would not be correct in saying that conclusion followed from what 
SOURCE said. However, SOURCE could have replaced his existential with 
a skolem constant ( a newly generated URI, guaranteed different from 
any other URI anywhere else) and, my claim is, that you would have 
been told virtually the same content by SOURCE under those 
circumstances as you would have been by SOURCE telling you his 
existential. (Not quite *exactly* the same, since you would know, in 
addition to the fact that the thing exists, that SOURCE was using 
this URI to refer to it. But that information wouldnt help you make 
any inferences about the thing that you couldnt have made from the 
existential.) But indeed, if someone signs a document then it isnt, 
in general, correct to transfer that signature to another document 
that differs even in the slightest respect, so the issue of whether 
the inferences are valid or not may be irrelevant here.


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Received on Tuesday, 24 July 2001 01:27:09 UTC

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