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Re: pfps-08 last call comment on typed literals

From: pat hayes <phayes@ai.uwf.edu>
Date: Thu, 3 Apr 2003 14:48:40 -0500
Message-Id: <p05111b0cbab2216eca33@[10.0.100.86]>
To: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>
Cc: bwm@hplb.hpl.hp.com, w3c-rdfcore-wg@w3.org

>From: Brian McBride <bwm@hplb.hpl.hp.com>
>Subject: Fwd: pfps-08 last call comment on typed literals
>Date: Thu, 20 Mar 2003 19:41:32 +0000
>
>>Date: Thu, 20 Mar 2003 18:56:18 +0000
>>To: pfps@research.bell-labs.com, www-rdf-comments@w3.org
>>From: Brian McBride <bwm@hplb.hpl.hp.com>
>>Subject: pfps-08 last call comment on typed literals
>>
>>Peter,
>>
>>You made a last call comment "Comment on Last Call Working Draft of RDF
>>Semantics document concerning typed literals" captured in
>>
>   http://www.w3.org/2001/sw/RDFCore/20030123-issues/#pfps-08
>>
>>After due consideration, the RDFCore WG has resolved
>>
>>[[RDFCore do not accept this comment. The semantics are as intended.  The
>>text has been clarified to make this clearer.]]
>>
>   http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2003Mar/0124.html
>>
>>
>>Please reply to this email, copying www-rdf-comments@w3.org indicating
>>whether this decision is acceptable.
>>
>>Brian McBride
>
>
>I do not view this reponse as acceptable because it does not point to the
>clarification text.  There may also remain outstanding action items related
>to this issue (namely pointing to Pat's message(s)).
>
>    http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2003Mar/0124.html
>  >
>  >
>  >Please reply to this email, copying www-rdf-comments@w3.org indicating
>  >whether this decision is acceptable.
>  >
>  >Brian McBride
>
>
>I also do not view this response as acceptable for technical reasons:
>
>1/
>
>  From http://www.w3.org/TR/2003/WD-rdf-mt-20030123/
>
>In an RDFS interpretation I (see section 3.3)
>          I(rdf:XMLLiteral) in ICEXT(I(rdfs:Datatype))
>In a D-interpretation, for any D (see Section 3.4)
>          ICEXT(I(rdfs:Datatype)) = D
>
>Therefore, in any D-interpretation, for any D, there must be a member of D
>that is a standard datatype corresponding to rdf:XMLLiteral.
>
>This means that any set of datatypes includes a datatype for
>rdf:XMLLiteral, and this datatype has a L2V mapping that takes lexical
>forms (in the form of strings *without* language tags) to resources.
>Any specification of D-interpretations must include this mapping.
>
>This superfluous mapping cannot be accessed from RDF, but can in OWL, for
>example by
>
>          rdf:XMLLiteral owl:sameIndividualAs ex:foo .
>          ex:bar ex:baz "55"^^ex:foo .
>
>I do not view this as an acceptable situation, if only for semantic
>cleanliness reasons.
>
>This situation is not improved in the current editor's draft.
>
>2/
>
>Even if this issue were to be solved, I believe that OWL should have the
>following sort of entailment hold:
>
>          rdf:XMLLiteral owl:sameIndividualAs ex:foo .
>          _:x owl:sameIndividualAs "..."@en^^rdf:XMLLiteral .
>          _:y owl:sameIndividualAs "..."@en^^ex:foo .
>
>entails
>
>          _:x owl:sameIndividualAs _:y .
>
>(This entailment holds for every URI reference except rdf:XMLLiteral.)
>
>However, there is no way for OWL to do this, because typed literals that
>include ex:foo are interpreted by the rules for non-built-in datatypes and
>there is no way to specify a non-built-in datatype that works the same way
>as rdf:XMLLiteral.
>
>I do not view this as an acceptable situation.

Peter, could you articulate *why* you do not view it as acceptable? 
It seems to me to be inevitable that the built-in datatype will 
differ from other datatypes since it has a unique relationship to 
lang tags in the syntax. As you say, there is no way to specify a 
non-built-in datatype that works the same way as the built-in 
datatype. That is why we built it in, because it needed to be treated 
specially.  The consequence for OWL is merely that OWL is required to 
respect the unique status of the built-in RDF datatype, which does 
not seem to me to be a severely onerous requirement on either OWL 
users or the OWL spec.

Allowing the entailment you describe would make the semantic picture 
somewhat more uniform, but it would also complicate the 
implementation in many ways. At present, an engine can take the 
presence of the datatype label "rdf:XMLLiteral" as a direct syntactic 
flag which indicates the need to parse lang tags in a particular way, 
without requiring any inference to be done. Since this treatment of 
lang tags is essentially a syntactic matter concerned with XML, to 
require all engines to indulge in open-ended OWL reasoning in order 
to check whether or not to proceed with a syntactic operation seems 
counterproductive to me.

One option would be to say that in a D-interpretation (not a simple 
RDF interpretation) , rdf:XMLLiteral should be a 'fully-fledged' 
datatype, so that the inference you describe above would hold. It 
would mean that ex:foo would be obliged to handle lang tags in the 
same way that rdf:XMLLiteral does, note, so that implementations 
would be obliged to check that any user-defined datatype was *not* 
equal to rdf:XMLLiteral before treating lang tags appropriately.  Let 
me know if that would be acceptable, and if so then I will put it to 
the WG as a suggested change. I do not think it will affect any 
documents other than the semantics, and has no real impact on RDF 
reasoning as such, so would be an easy change to make.

Pat
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Received on Thursday, 3 April 2003 14:49:50 EST

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