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Re: Two questions about bagid

From: Frank Manola <fmanola@mitre.org>
Date: Fri, 14 Feb 2003 09:35:43 -0500
Message-ID: <3E4CFEBF.3070006@mitre.org>
To: pat hayes <phayes@ai.uwf.edu>
CC: Tim Berners-Lee <timbl@w3.org>, w3c-rdfcore-wg@w3.org

pat hayes wrote:

> 
>> On Tuesday, Feb 11, 2003, at 16:17 US/Pacific, pat hayes wrote:
>>
>>>> On Tue, 11 Feb 2003, Tim Berners-Lee wrote:
>>>>
>>>>>  Another question is about the semantics.
>>>>>  I understand that an id  :i  on the statement  { :superman :can :fly}
>>>>>  should generate the statements
>>>>>
>>>>>  :i a rdf:Statement;  rdf:subject :superman;   rdf:predicate :can;
>>>>>  rdf:object :fly.
>>>>>  :superman :can :fly.
>>>>>
>>>>>  and I might want to use this to generate attribution:
>>>>>
>>>>>  :lois :thinks :i.
>>>>>
>>>>>  This would suggest that an owl reasoner (say) that knows that 
>>>>> :superman
>>>>>  and
>>>>>  :clarkekent are daml:equivalent should be able to infer that
>>>>>
>>>>>  :i a rdf:Statement;  rdf:subject : clarkekent;   rdf:predicate :can;
>>>>>  rdf:object :fly.
>>>>>  : clarkekent :can :fly.
>>>>>  :lois :thinks :i.
>>>>>
>>>>>  This seems counterintuitive, as one would expect it allow one to
>>>>>  conclude
>>>>>  that the modified statement is due to the original source.
>>>>>  Some form of quoting around the subject, predicate
>>>>>  and object would seem necessary.
>>>>
>>>
>>> Right. This arises from the way that RDF handles reification. The 
>>> obvious, and simplest, way to understand the above would be one where 
>>> the reification :i refers to the triple itself, ie to its syntactic 
>>> form, in effect quoting it.  Then the equality substitution would not 
>>> be valid, since even though :clarkekent = :superman, the *triples* 
>>> expressing the propositions that Clarke can fly, and that Superman 
>>> can fly, are distinct piece of syntax. But this way of understanding 
>>> reification was rejected by the WG in favor of one where the 
>>> reification is understood to refer to the things that the original 
>>> triple referred to, so that for example the subject of the reified 
>>> triple is not the subject NODE of the triple, but the thing that node 
>>> refers to, which is that same flying guy, no matter what name you use 
>>> to refer to him by. This might be called a de-re rather than a 
>>> de-dicto interpretation of reification. This allows equality 
>>> substitution, but it does not allow a reification to be coherently 
>>> used as a de-dicto object of a psychological modality like 'thinks' 
>>> or 'believes'.
>>>
>>> We could have gone either way on this. But we can't go both ways at 
>>> once.
>>
>>
>> What is not clear is the use of going with the de-re interpretation.
> 
> 
> Im not sure I can clearly recollect what led us to that choice, but I 
> know the matter was discussed at some length (though not using this 
> terminology). As I recall, Dan C. said that it should be interpreted 
> this way at least in part because there were use cases which required 
> it, but I can no longer bring the details to mind.
> 


I don't necessarily mean to suggest that we go back through all this 
again, but the pertinent threads where we discussed this were places 
like the following, in case anyone wants to go through the archives 
(including de re/de dicto, Superman, and the whole nine yards):

http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2002Jan/0157.html
http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2002Feb/0314.html
http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2002Feb/0239.html

--Frank

-- 
Frank Manola                   The MITRE Corporation
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mailto:fmanola@mitre.org       voice: 781-271-8147   FAX: 781-271-875
Received on Friday, 14 February 2003 09:16:54 EST

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