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a few questions about literals

From: Pat Hayes <phayes@ai.uwf.edu>
Date: Wed, 27 Feb 2002 17:05:27 -0600
Message-Id: <p05101483b8a1f55ccb6b@[65.212.118.219]>
To: w3c-rdfcore-wg@w3.org
Guys, I started drafting a new version of the MT to reflect our 
staked-down decision that literals always denote themselves. This 
simplifies (and clarifies) the graph syntax and the basic MT,  but it 
could be done in several different ways, so I wonder if anyone has 
any strong views on any of the following question: should we allow 
literals to entail bnodes ?

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 .

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?

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. 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

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Received on Thursday, 28 February 2002 11:53:53 EST

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