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Re: Simplified proposal for string literals

From: Pat Hayes <phayes@ihmc.us>
Date: Wed, 18 May 2011 13:54:16 -0500
Cc: RDF Working Group WG <public-rdf-wg@w3.org>
Message-Id: <544B93F6-46CF-4D93-959E-F052D0A82645@ihmc.us>
To: Pierre-Antoine Champin <pierre-antoine@champin.net>

On May 18, 2011, at 12:32 PM, Pierre-Antoine Champin wrote:

> I think I like proposal B as well.
> 
> Just a thought, though:
> 
> shouldn't we use another name than PlainLiteral for "literals with
> language tag" ?

Yes, I (now) tend to agree. I was trying to avoid terminology-bloat, but the confusion isnt worth it. How about rdf:Word or rdf:Text for a literal with a language tag? To distinguish a word in a language from a mere string, is the idea.

Pat

> 
> First, this is not exactly the same as the actual rdf:PlainLiteral datatype.
> 
> Second, the term "plain literal" currently applies to both literals with
> and without a language type, and I don't think changing that is a
> reasonable option (will conflict with common use, existing documents,
> not to mention recommendations such as SPARQL).
> 
>  pa
> 
> 
> On 05/18/2011 12:57 AM, Pat Hayes wrote:
>> As my proposed extension to rdf:PlainLIteral seems to have fallen on deaf ears, allow me to suggest a simplified version of it which might be more acceptable. There are two versions. In the first, plain literals are no longer strings. so the current equivalence between "string" and "string"^^xsd:string no longer applies. The second keeps this equivalence. 
>> 
>> Veraion A
>> 
>> 1.  rdf:PlainLIteral is a unique special datatype, built into basic RDF (along with rdf:XMLLIteral) with a special, unique formulation. It applies to plain literal syntax, which is thought of as specifying a pair of a string and a language tag. If no language tag is present, then the language tag of the literal is 'NULL'. The L2V mapping of this datatype takes the pair <string, tag> to itself, ie it is the identity mapping on these pairs. 
>> Put another way, the datatype value of "string" is <string, NULL> and of "string"@tag is <string, tag>. 
>> Every plain literal in RDF has the datatype rdf:PlainLIteral, even though this name is not used explicitly in the literal syntax. 
>> 
>> 2. rdf:PlainLIteral MUST NOT be used as an explicit datatype name in any RDF literal of the form "string"^^datatype. LIterals of the form "string@tag"^^rdf:PlainLiteral MUST be rewritten as a plain literal "string"@tag or flagged as an error.
>> 
>> 3. "string" is no longer sameAs "string"^^xsd:string (the first has a NULL language tag, the second has no tag at all.) 
>> 
>> Version B
>> 
>> 1.  rdf:PlainLIteral is a unique special datatype, built into basic RDF (along with rdf:XMLLIteral) with a special, unique formulation. It applies to plain literal syntax, which is thought of as specifying either a character string, or a pair of a string and a language tag.  The L2V mapping of this datatype takes both strings and pairs <string, tag> to themselves, ie it is the identity mapping on strings and on pairs. 
>> Put another way, the datatype value of "string" is  string  and of "string"@tag is <string, tag>. 
>> Every plain literal in RDF has the datatype rdf:PlainLIteral, even though this name is not used explicitly in the literal syntax. 
>> 
>> 2. rdf:PlainLIteral MUST NOT be used as an explicit datatype name in any RDF literal of the form "string"^^datatype. LIterals of the form "string@tag"^^rdf:PlainLiteral MUST be rewritten as a plain literal "string"@tag or flagged as an error.
>> 
>> 3. "string" and "string"^^xsd:string are equivalent, so to avoid equality reasoning, the datatype xsd:string is deprecated in RDF. RDF SHOULD NOT use xsd:string as a datatype in typed literals, and applications MAY rewrite any literal typed with xsd:strong as a plain literal with no language tag. 
>> 
>> --------
>> 
>> Either way, this keeps existing plain literal syntax exactly as it is at present, does not require anyone to rewrite any up-front code, and retains the rdf:PlainLIteral typing without getting involved with the trailing-@ messiness. It  requires one exception in the RDF semantics to allow this slightly nonstandard datatype, but I don't think this is of any importance at all, especially as the L2V mapping is so trivial. It will require short changes to Concepts and Semantics, and a quick check over Testcases, but we will be doing this anyway. 
>> 
>> FWIW, I marginally prefer  version B, as it settles the xsd:string business once and for all. But only marginally.
>> 
>> Pat
>> 
>> 
>> 
>> ------------------------------------------------------------
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>> 
>> 
>> 
>> 
>> 
>> 
>> 
> 
> 

------------------------------------------------------------
IHMC                                     (850)434 8903 or (650)494 3973   
40 South Alcaniz St.           (850)202 4416   office
Pensacola                            (850)202 4440   fax
FL 32502                              (850)291 0667   mobile
phayesAT-SIGNihmc.us       http://www.ihmc.us/users/phayes
Received on Wednesday, 18 May 2011 18:54:51 GMT

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