W3C home > Mailing lists > Public > w3c-rdfcore-wg@w3.org > February 2003

RE: language tags in typed RDF literals

From: pat hayes <phayes@ai.uwf.edu>
Date: Wed, 12 Feb 2003 10:52:22 -0600
Message-Id: <p05111b02ba702b725fbc@[10.0.100.86]>
To: <Patrick.Stickler@nokia.com>
Cc: w3c-rdfcore-wg@w3.org

>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.

I'm sympathetic to that idea, but I think that is just a cosmetic 
change to the wording. The semantics has to treat the built-in 
datatype as a special syntactic case already. The real issue remains: 
lang tags in typed literals are allowed by the syntax, but required 
to be meaningless by the semantics, which seems dumb.  Either we 
should get rid of them in the syntax, or we should let them be at 
least potentially meaningful in the semantics.

Pat

>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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>>
>>


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Received on Wednesday, 12 February 2003 11:52:26 EST

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