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Re: Proposal for ISSUE-12, string literals

From: Andy Seaborne <andy.seaborne@epimorphics.com>
Date: Sat, 14 May 2011 16:44:29 +0100
Message-ID: <4DCEA35D.6030406@epimorphics.com>
To: public-rdf-wg@w3.org


On 13/05/11 22:37, Steve Harris wrote:
> On 2011-05-13, at 19:20, Alex Hall wrote:
> ...
>> 3. There are probably countless instances of the following logic deployed in existing systems (I cut-and-pasted this directly from my own code):
>>
>> public Literal(String lexicalValue, String language, URI datatype) {
>>    ...
>>    if (language != null&&  datatype != null) {
>>      throw new IllegalArgumentException("An RDF literal may not have both a language and a datatype.");
>>    }
>>    ...
>> }
>>
>> I'm willing to change my code, but I can't speak for everybody...
>
> More concerning is code like:
>
> Literal(String lexicalValue, Resource lang_or_dt)
> {
> 	if (typeof(lang_or_dt) == Literal) {
> 		/* it has a language tag */
> 	} else if (typeof(lang_or_dt) == URI) {
> 		/* it has a datatype */
> 	} else {
> 		/* it has neither */
> 	}
> }
>
> We have a lot of such code.

Same - the "either-or" pattern is the normal way to process literals.

> It /might/ all come out in the wash, but it's going to need some care.
>
> - Steve
>

A possible interaction with RDF/XML:

------------------
@prefix  : <http://example/> .
@prefix xsd:     <http://www.w3.org/2001/XMLSchema#> .

:x :p "foo"@en .
:x :q "foo"^^xsd:string .
:x :r 1 .
------------------

can be written in RDF/XML as:
------------------

<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE RDF [
   <!ENTITY xsd "http://www.w3.org/2001/XMLSchema#">
]>

<rdf:RDF
     xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
     xmlns="http://example/"
     xmlns:xsd="&xsd;">
   <rdf:Description rdf:about="http://example/x" xml:lang="en" >
     <p>foo</p>
     <q rdf:datatype="&xsd;string">foo</q>
     <r rdf:datatype="&xsd;integer">1</r>
   </rdf:Description>
</rdf:RDF>
------------------

that is, with the xml:lang not on the literal but further out in the XML 
because xml:lang propagates inwards.

What happens to the xsd:string? Either existing RDf changes or RDF/XML 
can't write langs on xsd:string?  I don't think we can insist the 
xml:lang has to be directly on the xsd:string element because that's not 
how XML works (as I understand it).

	Andy
Received on Saturday, 14 May 2011 15:45:13 GMT

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