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Re: Possible tweak to datatype semantics

From: Sandro Hawke <sandro@w3.org>
Date: Fri, 13 Sep 2013 08:57:56 -0400
Message-ID: <52330BD4.4000706@w3.org>
To: "Peter F. Patel-Schneider" <pfpschneider@gmail.com>
CC: Pat Hayes <phayes@ihmc.us>, RDF WG <public-rdf-wg@w3.org>, Antoine Zimmermann <antoine.zimmermann@emse.fr>
On 09/13/2013 02:03 AM, Peter F. Patel-Schneider wrote:
> 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.
>

Assuming you mean "if inertia was NOT strongly indicating".

To my mind, this change is a simple bug fix, not unreasonable to do 
after Last Call.   I could be wrong about that.


> 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 .
> but
>   :a :p "foo"^^x:dt .
> does.
>

As a human, that seems perfectly correct to me.   When I see the empty 
graph, I do not know that x:dt is an rdfs:Class.  When I see :a :p 
"foo"^^x:d, I do.   Just like I also know :p is an rdf:Property when I 
see that triple.

> 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.
>

I don't think that's actually Pat's argument.    I understood the 
argument to be that this change makes the formal semantics more closely 
match human intuition.   Not to be provocative, but I though that was 
the goal of formal semantics -- to match human intuition as much as 
possible while still being completely precise and being fairly simple 
and comprehensible.

> 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 rdfs:Literal.
>

Perhaps this is relevant to the argument you think/thought Pat was 
making; I don't see its relevance.

        -- Sandro


> peter
>
> 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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>>
>>
>>
>>
>>
>>
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Received on Friday, 13 September 2013 12:58:02 UTC

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