W3C home > Mailing lists > Public > w3c-rdfcore-wg@w3.org > February 2002

Re: a few questions about literals

From: Dan Connolly <connolly@w3.org>
Date: 28 Feb 2002 13:49:12 -0600
To: Pat Hayes <phayes@ai.uwf.edu>
Cc: w3c-rdfcore-wg@w3.org
Message-Id: <1014925753.2453.15.camel@jammer>
On Wed, 2002-02-27 at 17:05, Pat Hayes wrote:
[...]
> At present, a graph entails its existential generalization which is 
> gotten by 'erasing' urirefs into bnodes, eg
> 
> ex:Jenny ex:age what:ever .  |=    ex:Jenny ex:age _:x .
> 
> Do we want this to be true for literals as well? Eg should this be a 
> valid inference?
> 
> ex:Judy ex:age "10" .   |=      ex:Judy ex:age _:x .

yes.

It is in our "swap" software. I can make test cases if
anybody likes.


> It seems to me that we should do this, since there is no doubt that 
> literals do denote something - themselves, in fact - in any 
> interpretation.
> 
> This means that the following inference would be valid, for example:
> 
> ex:Jenny ex:age "10" .   |=    ex:Jenny ex:age _:y .
> 
> which might seem a bit worrying if there was an rdfs:drange assertion 
> around, eg
> ex:age rdfs:drange xsd:number
> which imposes the 'lexical' datatype in the first case, but looks 
> like it might impose the 'value' in the second case; but in fact it 
> is OK, since that conclusion would only trigger the value datatyping 
> constraint if the bnode were also the subject of rdfs:dlex; and that 
> in turn would require the original graph to have had something like 
> this in it:
> 
> ex:Jenny ex:age "10"  .
> "10" rdfs:dlex "12" .
> 
> which is so crazy that no-one should be surprised if it has crazy 
> entailments, right?

right.

> Anyway, if y'all agree that we should accept this inference, then I 
> think the simplest way to re-do the MT is to simply say up-front that 
> *all* RDF interpretations must include *all* literals in their 
> universe.

yup; that seems straightforward.

> Then we can just say that for literals E, I(E) = E, and not 
> talk about things like LV and XL at all. Does anyone have any 
> philosophical objections to this? It would allow quite a few of the 
> lemmas to be stated with fewer qualifications, and the proofs to be 
> simplified.
> 
> Pat
> 

-- 
Dan Connolly, W3C http://www.w3.org/People/Connolly/
Received on Thursday, 28 February 2002 14:49:14 EST

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