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RE: N3 and N-Triples (was: RDF in HTML: Approaches)

From: Graham Klyne <GK@ninebynine.org>
Date: Thu, 06 Jun 2002 12:03:53 +0100
Message-Id: <5.1.0.14.2.20020606115238.03859050@joy.songbird.com>
To: "Seaborne, Andy" <Andy_Seaborne@hplb.hpl.hp.com>
Cc: "'RDF Interest'" <www-rdf-interest@w3.org>

At 10:51 AM 6/6/02 +0100, Seaborne, Andy wrote:
>If an RDF processor reads in the same file twice, are the bNodes the same or
>different?

I'd say "different".

>For compatibility with current RDF syntax, implicit bNodes in the current
>syntax yield different bnodes in the graph created.  But there is a choice
>as to whether an explicit bNode (one labeled in the syntax) is scoped to the
>file read operation (and hence creates different bNodes) or whether they get
>unique labels in the disjoint space.
>
>If RDF is to be exchanged between systems across a newtork using a
>serialization then the latter is desirable.  It means part of the system (an
>RDF application) on one machine can talk about the bNodes on another machine
>(the source of the graph).

That sounds rather dodgy to me -- the model theory is quite clear that 
bnodes are not identified with anything outside the graph in which they 
appear -- if you start introducing identifiers that describe bNodes from 
"outside", you (a) need to have a way of scoping them to a particular graph 
instance, or (b) be very sure that they are unique.

Because of the way that bNode semantics are defined (essentially, as 
existential variables), I don't think it really matters if you have 
different bnodes in different places as long as the associated statements 
about them are "isomorphic" -- there's some recent discussion in the DAML 
list about "minimal identifying description" (MID) between Richard Fikes 
and Peter Patel-Schneider that might have some bearing.   I don't know 
where the web archive is, but look for messages starting about:

[[
Date: Fri, 24 May 2002 15:39:41 -0700
From: Richard Fikes <fikes@ksl.stanford.edu>
To: Joint Committee <joint-committee@daml.org>
Subject: New DQL Specification
Content-Type: multipart/mixed;
  boundary="------------C8A05097584B9E8F59A89C7A"
]]

#g


-------------------
Graham Klyne
<GK@NineByNine.org>
Received on Thursday, 6 June 2002 07:18:43 GMT

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