W3C home > Mailing lists > Public > public-rdf-wg@w3.org > May 2011

Simplified proposal for string literals

From: Pat Hayes <phayes@ihmc.us>
Date: Tue, 17 May 2011 17:57:30 -0500
Message-Id: <237A93C7-7793-4592-8707-9C80DCAC827D@ihmc.us>
To: RDF Working Group WG <public-rdf-wg@w3.org>
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



------------------------------------------------------------
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 Tuesday, 17 May 2011 22:58:08 GMT

This archive was generated by hypermail 2.3.1 : Tuesday, 26 March 2013 16:25:42 GMT