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Re: Datatypes and xml:lang

From: Pat Hayes <phayes@ai.uwf.edu>
Date: Wed, 6 Feb 2002 12:45:00 -0600
Message-Id: <p0510143cb88725f8e3b6@[65.212.118.208]>
To: Patrick Stickler <patrick.stickler@nokia.com>
Cc: w3c-rdfcore-wg@w3.org
>
>I think that this would be the same representation in the
>convergence TDL/S-P model.
>
>I.e.
>
>    <rdf:Description rdf:ID="MyBook">
>       <dc:title xml:lang="en" rdf:value="The Tao of Poo"/>
>    </rdf:Description>
>
>gives us
>
>   MyBook dc:title _:1 .
>   _:1 rdf:value "The Tao of Poo" .
>   _:1 xml:lang _:2 .
>   _:2 rdf:value "en" .
>
>which combined with the presumed range constraint
>
>   xml:lang rdfs:range xsd:lang .
>
>entails
>
>   MyBook dc:title _:1 .
>   _:1 rdf:value "The Tao of Poo" .
>   _:1 xml:lang _:2 .
>   _:2 rdf:value "en" .
>   _:2 rdf:dtype xsd:lang .
>
>Note that the bNode preserves the context of
>the language attribution. Other contexts may
>associate the same literal with different languages.
>
>Eh?
>
>[Note that the literal contraction transformation
>means that in the graph/triples the only property
>that will actually have a literal as its value will
>be rdf:value]

Right, see my earlier message on the 'basis for convergence' thread.

I agree entirely about the above, and would add one comment: there is 
a general  RDF design principle at work here. If you want to say 
things about an entity which come in 'groups', like (A and B) or (D 
and E) , but where it wouldn't make sense to assert both of A and D, 
so you want to avoid getting things muddled up, then you have to 
introduce nodes (probably bnodes) to attach each group of properties 
to, and then express the combination as a conjunction of 
possibilities, using a special 'weak' property to express the 
possibility (which can usually be read as something like 'this could 
be one of those'). This is a general trick for encoding an and/or 
tree in an and tree (which is all we have in RDF). So applying that 
to the case 'looks like this literal' plus 'is written in French' and 
'looks like this other literal' plus 'is written in English', gives 
you the above.

Might be worth putting this idea in a primer somewhere, with some 
neat examples to make the point before introducing literals (?)

>
>--
>
>Additional issue:
>
>I think it is also necessary to clarify the relationship
>between xml:lang and xsd:lang, as it seems that the latter
>is the range of the former, but this has never been
>explicitly defined.

In the OMG MT,
aaa rdf:type rdf:Datatype .
would entail
aaa rdf:range aaa .
which may seem odd but is required to allow both subproperty of 
rdf:value and also range/type assignments. And it does make semantic 
sense in the MT.

So with this convention, I think that using either xml:lang or 
xsd:lang as an RDF datatype will implicitly assume that they are 
treated as identical as far as RDF is concerned.

Pat
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Received on Wednesday, 6 February 2002 13:44:24 EST

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