W3C home > Mailing lists > Public > semantic-web@w3.org > October 2007

Re: representing null in semantic frameworks

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Mon, 22 Oct 2007 04:02:11 -0400 (EDT)
Message-Id: <20071022.040211.159626016.pfps@research.bell-labs.com>
To: alanruttenberg@gmail.com
Cc: henry.story@bblfish.net, garret@globalmentor.com, semantic-web@w3.org

Wouldn't it be more direct to just say that a property (e.g., Pname) has
no values (for all members of a class or for an individual), as in 

	restriction(Pname cardinality(0))

or

	Individual(John type(restriction(Pname cardinality(0))))

peter



From: Alan Ruttenberg <alanruttenberg@gmail.com>
Subject: Re: representing null in semantic frameworks
Date: Sat, 20 Oct 2007 19:37:22 -0400

> rdf:nil is something, specifically the empty collection.
> 
> However, there is owl:Nothing, the empty class. If you say, for  
> instance, that some property has allValuesFrom owl:Nothing, then it  
> can't have any value. There is no thing which is rdf:type owl:Nothing.
> 
> -Alan
> 
> On Oct 20, 2007, at 12:25 PM, 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 Monday, 22 October 2007 08:10:16 GMT

This archive was generated by hypermail 2.3.1 : Tuesday, 26 March 2013 21:45:18 GMT