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Re: Simplified proposal for string literals

From: Nathan <nathan@webr3.org>
Date: Wed, 18 May 2011 11:28:02 +0100
Message-ID: <4DD39F32.8070208@webr3.org>
To: Pat Hayes <phayes@ihmc.us>
CC: RDF Working Group WG <public-rdf-wg@w3.org>
Hi Pat,

I admit I've lost track of this now very long thread, however is there a 
reason why we don't simply swap out language tags for IRIs which denote 
a string in a particular language, where each language resource is a 
subtype of xsd:string, where the @lang is syntax sugar, and where the 
lack of any @lang indicates that the type is xsd:string.

  "foo"@en -> TypedLiteral( "foo", rdf-lang:en )
    entails -> TypedLiteral( "foo", xsd:string )

  "foo" -> TypedLiteral( "foo", xsd:string )

Pretty sure I'll have missed a detail as to why this isn't possible / 
viable though.

FWIW, I did like your rdf:PlainLiteralString proposal, and failing that 
(B) from below.

Best,

Nathan

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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Received on Wednesday, 18 May 2011 10:28:54 GMT

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