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Re: RDF Model Theory Working Draft: Comment

From: Graham Klyne <GK@ninebynine.org>
Date: Sun, 07 Oct 2001 18:20:12 +0100
Message-Id: <5.1.0.14.2.20011007174720.040a2450@joy.songbird.com>
To: Arjun Ray <aray@nyct.net>
Cc: <www-rdf-comments@w3.org>
At 11:03 AM 10/7/01 -0400, Arjun Ray wrote:
>: the correspondence between an ntripleDoc and an RDF graph is that
>: the graph has one node for each uriref, bNode or literal identifier
>: in the document
>
>would lead me to expect that any graph-like picture should exhibit
>three nodes, one each for foo, bar and baz, because each one of them
>is a 'uriref, bNode or literal identifier'. ...

[...]

>... In 'the graph has one
>node for each uriref, bNode or literal identifier', does 'for each'
>mean 'not all'?

Ah, I see what you mean.  I'm not sure if that is an accurate statement of 
what was intended, but assuming that it was...

The fact that the uriref used to label an arc also has a corresponding node 
in the graph doesn't mean that the node itself *is* the arc.  I think the 
confusion here is caused by the existence of two distinct syntaxes for RDF:

- one is triple-based, in which the members of the triple are URIs or 
literals or bNodes that denote RDF resources and/or literal values,

- one is graph based, in which the graph nodes and arcs are defined 
independently of the urirefs or literals that may be used to label them.

Thus, assuming the quoted statement above to be exactly true, a graph 
consisting of the single statement:

     My:Subject My:property My:Object .

would contain three nodes and one arc thus:

     [My:Subject] --My:property--> [My:Object]

     [My:property]

In this case, the [My:property] *node* has no arcs to or from.  The model 
theory assigns truth values to a graph purely in terms of the arcs, so the 
existence of an isolated node has no effect on the graph's meaning;  thus, 
its presence in the graph may be regarded as moot.

#g


------------
Graham Klyne
GK@NineByNine.org
Received on Sunday, 7 October 2001 17:30:55 UTC

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