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Re: plain literals without language tag compare xsd:string in RDF

From: Pat Hayes <phayes@ihmc.us>
Date: Mon, 10 Mar 2008 12:30:03 -0500
Message-Id: <p06230902c3fb1e4868f5@[]>
To: Alan Ruttenberg <alanruttenberg@gmail.com>
Cc: "Williams, Stuart (HP Labs, Bristol)" <skw@hp.com>, public-awwsw@w3.org, "Carroll, Jeremy John" <jeremy.carroll@hp.com>, Sandro Hawke <sandro@w3.org>
At 10:16 AM -0500 3/8/08, Alan Ruttenberg wrote:
>All right, I see (RDF-MT) :
>>These rules may not provide a complete set of inference principles 
>>for D-entailment, since there may be valid D-entailments for 
>>particular datatypes which depend on idiosyncratic properties of 
>>the particular datatypes, such as the size of the value space (e.g. 
>>xsd:boolean has only two elements, so anything established for 
>>those two values must be true for all literals with this datatype.) 
>>In particular, the value space and lexical-to-value mapping of the 
>>XSD datatype xsd:string sanctions the identification of typed 
>>literals with plain literals without language tags for all 
>>character strings which are in the lexical space of the datatype, 
>>since both of them denote the Unicode character string which is 
>>displayed in the literal; so the following inference rule is valid 
>>in all XSD-interpretations. Here, 'sss' indicates any RDF string in 
>>the lexical space of xsd:string.
>>xsd 1a:  uuu aaa "sss" => uuu aaa "sss"^^xsd:string .
>>xsd 1b:  uuu aaa "sss"^^xsd:string => uuu aaa "sss".
>>Again, as with the rules rdfD2 and rdfD3, applications may use a 
>>systematic replacement of one of these equivalent forms for the 
>>other rather than apply these rules directly.
>Regrettably, SPARQL uses the RDFS syntactic equality in its 
>definition of equality for literals :(

There was a huge battle for the soul of SPARQL. On one view, the 
whole idea of a query is that it is entailed by the KB: to query a KB 
is to hold up a query pattern to it and say,in effect, show me all 
the ways you (semantically) entail some instance of that. On the 
other view, the task of a query is to act as a kind of fishing net 
for syntactic matches to a pattern, to suck out of the KB all the 
instances of the query pattern which actually occur in it, more or 
less; and that questions of entailment should be left to other 
engines to determine. As always in deep WG disputes, the final result 
is a compromise which tries to give at least a nod to all parties, 
and so fails to satisfy anyone completely. But the second, syntactic, 
criterion gives a finer-grained access to the actual contents of the 
KB, which is needed by many applications. For example, you might want 
to extract all the RDF triples which contain a typed literal. If 
SPARQL cannot distinguish untyped from xsd:typed literals, what is a 
meaningful response? Hence the tendency, in the spec, to use the more 
'surface'-oriented, syntactic, criteria where possible.

>I wonder what RIF is planning to do

Only a guess, But I expect RIF to be much more semantically oriented.


>On Mar 7, 2008, at 10:31 AM, Williams, Stuart (HP Labs, Bristol) wrote:
>>I raised you question with my colleague, Jeremy Carrol (Cc'd) who 
>>responded as follows:
>>They are identical
>>"foo" owl:sameAs "foo"^^xsd:string .
>>is necessarily true.
>>as recorded in the RDF Test Cases doc
>>In a further exchange he also confirmed/clarified that it is 
>>neccessarily the case that:
>>         "1234" owl:sameAs "1234"^^xsd:string .
>>ie. (I think) that means that:
>>         "1234" owl:sameAs "1234"^^xsd:integer .  ## or some other 
>>numeric datatype.
>>is necessarily false (which is what I would expect).
>>Hewlett-Packard Limited registered Office: Cain Road, Bracknell, 
>>Berks RG12 1HN
>>Registered No: 690597 England
>>>-----Original Message-----
>>>From: public-awwsw-request@w3.org
>>>[mailto:public-awwsw-request@w3.org] On Behalf Of Alan Ruttenberg
>>>Sent: 04 March 2008 15:29
>>>To: Pat Hayes
>>>Cc: public-awwsw@w3.org
>>>Subject: plain literals without language tag compare xsd:string in RDF
>>>Is there any utility to having these being disjoint classes?
>>>It would seem to me that it would be more sensible to say
>>>that any string that doesn't have a  language type or a
>>>datatype is inferred to be of type xsd:string.
>>>Did this situation come about because it was easier to make
>>>the RDF semantics look cleaner, or was there some principled
>>>reason for making the distinction?

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Received on Monday, 10 March 2008 17:30:21 UTC

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