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Re: Proposal for ISSUE-12 language-tagged literals

From: Richard Cyganiak <richard@cyganiak.de>
Date: Thu, 14 Jul 2011 14:08:07 +0100
Cc: public-rdf-wg@w3.org
Message-Id: <BDDECDF3-28EE-41AA-86D0-BA1BE6D24309@cyganiak.de>
To: antoine.zimmermann@insa-lyon.fr
On 14 Jul 2011, at 08:36, Antoine Zimmermann wrote:
> In your proposal, rdf:Text is equivalent to rdf:PlainLiteral so it seems redundent.

No. rdf:Text is a class, rdf:PlainLiteral is a datatype.

Using rdf:PlainLiteral with rdfs:range creates expectations that its impractical lexical form is used.

"Plain literals without language tag" are now simply xsd:strings. "Plain literals with language tag" are not actually plain. So the name "plain literal" doesn't make sense any more.

For these reasons, rdf:PlainLiteral is inadequate for use in rdfs:range statements.

Best,
Richard



> Moreover, rdf:PlainLiteral was originally called rdf:text (see http://www.w3.org/TR/2009/WD-rdf-text-20090421/ for instance) but this name was rejected because the concept of "text" includes many other features like directionality, font, structure, etc.
> I suggest some changes below:
> 
> Le 13/07/2011 16:51, Richard Cyganiak a écrit :
>> We have addressed one half of ISSUE-12, the half about string literals *without* language tags.
>> 
>> Here's a proposal for the other half, string literals *with* language tags and rdf:PlainLiteral. This is a very minimalist proposal.
>> 
>> Summary:
>> - add classes rdf:LangString and rdf:Text so we can better specify string literals as rdfs:range of properties
> 
> don't add rdf:Text.
> 
>> - add the technical term “language-tagged string” as an alternative to the current “plain literal with language tag”
>> - ask OWL and RIF WGs to update rdf:PlainLiteral document to reflect the RDF WG decisions
>> 
>> (This completes my ACTION-62.)
>> 
>> Best,
>> Richard
>> 
>> 
>> [[
>> 
>> A literal is either a typed literal or a language-tagged string.
>> 
>> A language-tagged string is an<Unicode string, language tag>  pair.
>> 
>> "Plain literal with language tag" (from RDF 2004) is an alternative term for "language-tagged string". They are the same thing.
>> 
>> rdf:LangString is the class of all language-tagged strings. It can be used in rdfs:range statements.
>> 
>> rdf:Text is the class of all language-tagged strings and all Unicode strings. It can be used in rdfs:range statements.
> 
> remove this line.
> 
>> The RDF Concepts document is updated with the definitions above. No other changes to RDF Concepts.
>> 
>> The RDF Semantics document is updated to make rdf:LangString and rdf:Text work. No other changes to RDF Semantics.
> 
> remove "and rdf:Text"
> 
>> The RDF Schema document is updated to add rdf:LangString and rdf:Text. No other changes to RDF Schema.
> 
> remove "and rdf:Text"
> 
>> The SPARQL WG is asked to *consider* whether DATATYPE("foo"@en) should return rdf:LangString instead of error.
> 
> if rdf:LangString is not a datatype, then I think SPARQL should'nt return it. Does SPARQL return rdfs:Literal?
> 
>> The OWL and RIF WGs are asked to make changes to the rdf:PlainLiteral specification:
>> 
>> - Clarify that the purpose of the document is *solely* to provide
>>   compatibility between RDF and specifications whose literal
>>   design does not support language tags.
> 
> It is not the only purpose of rdf:PlainLiteral. The essential purpose, AFAIK, is to allow systems to type all literals. It also makes possible the definition of complex datatypes (for instance, it is possible to define a datatype equivalent to your rdf:LangString, or to the English-tagged strings, etc). Without a proper datatype for that, such definitions are not possible.
> 
>> - The spec should be changed to *only* cover strings *with* language
>>   tags, because strings without language tags now always have a
>>   datatype (xsd:string) and therefore don't need to be covered in this
>>   spec.
>> 
>> - Instead of defining its complete own datatype rdf:PlainLiteral,
>>   the spec should only extend the rdf:LangString class so that
>>   it can serve as a datatype.
>> 
>> ]]
> 
> 
> -- 
> Antoine Zimmermann
> Researcher at:
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> 
Received on Thursday, 14 July 2011 13:08:39 GMT

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