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RE: language tags in typed RDF literals

From: <Patrick.Stickler@nokia.com>
Date: Wed, 12 Feb 2003 12:03:37 +0200
Message-ID: <A03E60B17132A84F9B4BB5EEDE57957B01B90B2B@trebe006.europe.nokia.com>
To: <phayes@ai.uwf.edu>, <www-rdf-comments@w3.org>
Cc: <bwm@hplb.hpl.hp.com>, <Jan.Grant@bristol.ac.uk>


A third option is that the lang tag is not significant to XMLLiteral,
or that XMLLiteral is not treated as a datatype, but as a third type
of literal, as it used to be, either of which would be my preferance.

I.e. the problem is with XMLLiteral, and the correction should be
to XMLLiteral.

Patrick

> -----Original Message-----
> From: ext pat hayes [mailto:phayes@ai.uwf.edu]
> Sent: 12 February, 2003 02:01
> To: www-rdf-comments@w3.org
> Cc: bwm@hplb.hpl.hp.com; Jan.Grant@bristol.ac.uk
> Subject: language tags in typed RDF literals
> 
> 
> 
> The current design of RDF literals is needlessly complicated and kind 
> of silly.  The syntax allows language tags to occur in typed 
> literals, but in all cases other than rdf:XMLLiteral, these tags are 
> required to have no meaning, so the semantics is obliged to provide a 
> valid inference rule which allows any language tag in any such typed 
> literal to be removed or replaced by any other.  This considerably 
> complicates the statement of the semantics, adds a burden to any 
> implementation, nullifies the implicit design principle that literals 
> can be compared for identity using simple lexical matching (since an 
> engine is required to strip out all such lang tags while performing 
> inferences or checking for identity), and provides no useful 
> expressive function.
> 
> A related point is that the requirement in the semantics that 
> datatypes other than rdf:XMLLiteral *must* ignore language tags seems 
> to restrict possible future datatyping proposals needlessly.
> 
> I suggest therefore that
> 
> EITHER
> 
> (1) lang tags be forbidden by the RDF syntax from appearing in 
> non-XML typed literals.
> 
> OR ELSE
> 
> (2) the notion of the lexical space of a datatype be generalized to 
> allow (not require)  lang tags to be taken into consideration by a 
> datatype, so that the lexical space may be a set of strings or pairs 
> of strings, i.e. a set of simple literals. This would have the effect 
> that it would no longer be valid to make arbitrary changes to a lang 
> tag in any literal, typed or not. It would also bring the treatment 
> of all RDF datatypes into alignment so that rdf:XMLLiteral need not 
> be considered a special case.
> 
> Either of these changes will simplify the semantics and make it more 
> coherent, but in slightly different ways.
> 
> Either change will produce fewer inference rules and lead to less 
> processing in a reasoning engine.
> 
> Pat Hayes
> -- 
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Received on Wednesday, 12 February 2003 05:03:42 GMT

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