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Re: blank nodes question

From: Peter P. Jones <ppj@concept67.fsnet.co.uk>
Date: Mon, 28 Jul 2003 20:11:36 +0100
To: Bob MacGregor <macgregor@ISI.EDU>, Graham Klyne <GK@ninebynine.org>, "Peter P. Jones" <ppj@concept67.fsnet.co.uk>, www-rdf-interest@w3.org
Message-ID: <3F258378.225.696E97@localhost>

On 27 Jul 2003 at 19:32, Bob MacGregor wrote:

> At 10:03 AM 7/27/2003 +0100, Graham Klyne wrote:
> 
[snip]
> >
> >There is, I think, a sustainable argument that blank nodes are not
> >*necessary*.
> 
> I beg to differ.  Blank nodes are absolutely necessary.
> 
> Consider translating an XML file into RDF, where typically
> none of the incoming resource nodes have URI's.  You have two choices,
> you can use blank nodes to represent them, or you can use (globally
> unique) URI's.  If you use URI's, then you need a scheme for
> generating them so that (1) you don't clash with other uniquely
> generated nodes, (2) you need to figure out how to label the nodes
> each of the subsequent times that you load the same graph, (3) you
> still need a scheme to know that these nodes are semantically "blank",
> so that your application can avoid generating "pointers" to them.  Its
> not safe to reference the URI's of blank nodes, since typically they
> won't recur the next time you load, or if they do recur, there is no
> way to guarantee that they denote the same node they did the first
> time.

But if nodes in the incoming XML file aren't namespaced (providing 
URIs) then what's wrong with using the address the resource was 
retrieved from to create the URIs? Surely that improves on blank 
nodes in that case....?

That's a different point from the original aim of my question which 
is why does the RDF model need blank nodes?
Jeremy Carroll spoke to that in a sense, but if there are never any 
blank arcs in RDF, why not just make use of the arc labelling instead 
of generating blank nodes?

[snip]
Received on Monday, 28 July 2003 15:13:48 GMT

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