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Re: representing null in semantic frameworks

From: Frank Manola <fmanola@acm.org>
Date: Sat, 20 Oct 2007 15:36:55 -0400
Message-Id: <0226B0C3-BD33-497B-8D52-8E5D584EDB98@acm.org>
Cc: "'Garret Wilson'" <garret@globalmentor.com>, "'Story Henry'" <henry.story@bblfish.net>, "'Semantic Web'" <semantic-web@w3.org>
To: Mark Cidade <marxidad@marxidad.com>

I think these are different things.  owl:Nothing is a *class  
identifier* (whose class extension is the empty set), not something  
that can be used as the value of arbitrary properties, which is what  
I think Garret is looking for.


On Oct 20, 2007, at 3:00 PM, Mark Cidade wrote:

> What about owl:Nothing?
> http://www.w3.org/TR/2004/REC-owl-guide-20040210/#owl_Nothing
> Mark
> -----Original Message-----
> From: semantic-web-request@w3.org [mailto:semantic-web- 
> request@w3.org] On
> Behalf Of Garret Wilson
> Sent: October 20, 2007 12:40 PM
> To: Story Henry
> Cc: Semantic Web
> Subject: Re: representing null in semantic frameworks
> Right. rdf:nil is an instance of rdf:List that is used to say  
> something
> like, "the next list of this linked list is really no list at  
> all" (i.e.
> L rdf:rest rdf:nil; see <http://www.w3.org/TR/rdf-schema/#ch_nil>).
> So in other words RDF created a special null value that is only valid
> for use with rdf:List. Does anyone know of any meeting minutes or  
> other
> documents that unveil why the WG didn't create a more general null  
> that
> you could use for anything?
> Thanks, Henry.
> Garret
> Story Henry wrote:
>> There is something close. rdf:Lists terminate with a null I think.
>> Henry
>> On 20 Oct 2007, at 18:15, Garret Wilson wrote:
>>> As RDF evolved, was there any discussion on adding an rdf:null
>>> resource---that is, a resource that represents no resource at all?
>>> One expected response: "My child, you're thinking like a programmer
>>> again---what you really want to do is assert the absence of any
>>> assertions regarding a particular subject and predicate, or you want
>>> to assume a closed world and just don't assert anything at all", or
>>> something like that---and I appreciate this point of view to some
>>> extent.
>>> But as a practical matter, let's say we have a list of baseball game
>>> scores. Wouldn't it be convenient for the resource at index 3 to be
>>> null to indicate that there was no score that week because there was
>>> a tornado that canceled the game?
>>> I'm not necessarily looking for a big online discussion. Just a  
>>> brief
>>> pointer to any reading on this subject would help. I'm sure there
>>> must have been some discussion of null over the development history
>>> of RDF.
>>> Thanks,
>>> Garret
Received on Saturday, 20 October 2007 19:37:27 UTC

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