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Re: Possible tweak to datatype semantics

From: Peter F. Patel-Schneider <pfpschneider@gmail.com>
Date: Thu, 12 Sep 2013 23:03:46 -0700
Message-ID: <5232AAC2.3010400@gmail.com>
To: Pat Hayes <phayes@ihmc.us>
CC: RDF WG <public-rdf-wg@w3.org>, Antoine Zimmermann <antoine.zimmermann@emse.fr>
What good would this change from the 2004 situation do?

Even if inertia was strongly indicating that this change should not be made, I 
would vote against it.

If you make this change, you have the situation that if x:dt is not a 
recognized datatype, the empty graph does not RDFS entail
   x:dt rdf:type rdfs:Class .
   :a :p "foo"^^x:dt .

I believe that your argument falls apart when you look closer at it.  You are 
saying, in effect, that if x:dt is a recognized datatype then any well-typed 
literal with it as the datatype belongs to it, and the appearance of an 
ill-typed literal causes a contradiction, and thus entails any graph, 
including the graph that states that the ill-typed literal belongs to the 
x:dt, so why not make this hold even if x:dt is not a recognized datatype. 
However, when x:dt is *not* a recognized datatype this reasoning doesn't hold 
water, so there is no reason to modify the semantics to make it valid.

You might just as well argue that if x:dt is a recognized datatype then it is 
a subclass of rdfs:Literal therefore anything should be a subclass of 


On 09/12/2013 10:25 PM, Pat Hayes wrote:
> I know its very late to even be talking about this, but Antoine's test cases made me notice an oddity which the current semantics for datatyped literals produces, and which would be easy to fix. So I'm outlining it here in case the WG feels it would be worth doing.
> We distinguish 'recognized' datatype IRIs from the others, and right now, if you see a literal with an unrecognized datatype IRI in it, say x:dt, then you know nothing at all about what that literal means. Absolutely nothing. So this inference:
> :a :p "foo"^^x:dt .
> |=
> :a :p _:x .
> _:x rdf:type x:dt .
> is not a valid entailment. But if x:dt were recognized, it would be: and moreover, you know this without knowing anything about x:dt. This entailment is valid for ANY recognized datatype, and ANY string "foo". So why isn't it valid for any datatype, recognized or not?  This is clearly slightly irrational. A rational way to reason would be: I know now, even without recognizing that datatype, that this inference will be valid when I do recognize it; and I won't need to know anything more about the datatype in order to make that inference; so why not just pretend that I recognize the datatype and make the inference now, to save time?
> We could fix this with the following changes.
> In section 7.1, add the condition (to the table, it would be the third line out of three):
> For any literal "sss"^^aaa, if IL("sss"^^aaa) is defined then <IL("sss"^^aaa), I(aaa)> is in IEXT(I(rdf:type))
> and add the explanatory text immediately below:
> "The third condition applies to all datatyped literals, whether the datatype IRI is recognized or not."
> And in section 7.2.1, at the beginning of the text, add the entailment pattern (moved from section 8.1.1, and with "for ddd in D" removed):
> rdfD1  <if S contains>  xxx aaa "sss"^^ddd  <then S D-entails> xxx aaa _:nnn .      _:nnn rdf:type ddd .
> together with its explanatory text from 8.1.1.
> The advantage to RDF engines is that this is one less case where they have to check whether or not a datatype is "recognized", and it means that the interpolation lemma is more useful when there are datatyped literals around.
> Any comments? Is this worth doing? Is this legally possible to do at this LC stage? I would be willing to declare the current version an error if that is what it takes :-)
> Pat
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Received on Friday, 13 September 2013 06:04:16 UTC

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