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Re: language tags in typed RDF literals

From: Brian McBride <bwm@hplb.hpl.hp.com>
Date: Thu, 13 Feb 2003 23:26:50 +0000
Message-Id: <5.1.0.14.0.20030213231557.02e9fe88@localhost>
To: pat hayes <phayes@ai.uwf.edu>, www-rdf-comments@w3.org
Cc: Jan.Grant@bristol.ac.uk

As I recall:

   - the WG has considered this.  At the time it made its decision, Pat 
advocated accepting that lang tags be allowed in the syntax, that it was 
harmless and seemed at the time to be important to Patrick who stated that 
Nokia felt strongly about the issue.

   - later Patrick reported that after further thought, that whilst Nokia 
still preferred the lang tag to be allowed in a datatyped literal, they 
could live without it.

Before last call, this is perhaps something we could have considered.  Now 
its a  change.  Might anyone change their review based on it?  Well, yes, 
it seemed important to Nokia.

How important is this Pat.  Is it worth a second last call?  If its just a 
case of extra work in writing the semantics - then I think you've made your 
bed.  If it has undesirable externally visible consequences, that might be 
different.

Brian

At 18:01 11/02/2003 -0600, pat hayes wrote:
>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 Thursday, 13 February 2003 18:25:45 GMT

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