Simplified proposal for string literals

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. 

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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 Tuesday, 17 May 2011 22:58:08 UTC