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Re: blank nodes question

From: Bob MacGregor <macgregor@ISI.EDU>
Date: Sun, 27 Jul 2003 19:32:13 -0700
Message-Id: <5.1.1.6.0.20030727192346.01b2aea0@tnt.isi.edu>
To: Graham Klyne <GK@ninebynine.org>, "Peter P. Jones" <ppj@concept67.fsnet.co.uk>, www-rdf-interest@w3.org

At 10:03 AM 7/27/2003 +0100, Graham Klyne wrote:

>At 20:01 26/07/03 +0100, Peter P. Jones wrote:
>
>>Hi,
>>
>>I have a question about blank nodes in RDF that's probably not as
>>naive as it sounds.
>>
>>Q: Why are blank nodes necessary?
>
>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.

So, you can have blank nodes, or you can have a maintenance
nightmare.  The choice is yours.

Cheers, Bob
Received on Sunday, 27 July 2003 22:32:29 GMT

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