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Re: Language-tagged strings

From: Antoine Zimmermann <antoine.zimmermann@emse.fr>
Date: Sat, 11 Aug 2012 14:45:56 +0200
Message-ID: <50265404.8070203@emse.fr>
To: Richard Cyganiak <richard@cyganiak.de>
CC: public-rdf-comments@w3.org
Richard,


I understand your concerns but currently, the pattern is:

"""
An 'X' consists of 'A', 'B'.
A 'Y' is an 'X' with 'B'=123 and it has an additional 'C'.
"""

These are two definitions, where the second refers to the first and 
contradicts it.

It should be, as you said:

"An X consists of A, B, and, if and only if B=123, C."

It is, I admit, difficult to phrase it in a way that is neither verbose 
nor unclear.

This is a proposal, I don't know if it's good enough:

"""
A literal in an RDF graph consists of:
  - a lexical form being a Unicode [UNICODE] string, which should be in 
Normal Form C [NFC],
  - a datatype IRI being an IRI that establishes the literal value.
  - and, if only if the datatype IRI is equal to 
http://www.w3.org/1999/02/22-rdf-syntax-ns#langString, a non-empty 
language tag as defined by [BCP47]. The language tag must be well-formed 
according to section 2.2.9 of [BCP47], and must be normalized to lowercase.

A literal that has a language tag is called a "language-tagged string".
"""

One more sentence could be added to ensure that the "if and only if" is 
well understood, for instance:

"So, a literal always has a lexical form and a datatype IRI, but does 
not have a language tag unless it is a language-tagged string, in which 
case it MUST have a language tag and the datatype IRI MUST be 
http://www.w3.org/1999/02/22-rdf-syntax-ns#langString."

I'm not sure it is necessary, though. I'm not either completely 
satisfied by the wording.


I hope this helps.
AZ.


Le 10/08/2012 19:18, Richard Cyganiak a écrit :
> Hi Antoine,
>
> On 10 Aug 2012, at 17:08, Antoine Zimmermann wrote:
>> The current Editor's draft of RDF Concept (as of 5th June 2012 [1])
>> defines a language-tagged string as literal [2]. By the definition
>> of literal above, this means that a language-tagged string consists
>> of: - a lexical form being a UNICODE string; - a datatype IRI.
>>
>> But it immediately contradicts this by saying that, in addition to
>> lexical form and datatype IRI, it also has a non-empty language
>> tag.
>
> It doesn't contradict itself. You have just stopped reading halfway
> through the definition of "literal".
 >
> The form of the statement is: "An X consists of A, B, and, if and
> only if B=123, C." You only read: "An X consists of A, B", and then
> claimed that the rest is contradictory.
 >
> Now it could be rephrased to: "An X is either an X1 or an X2. An X1
> consists of A and B; and B must not be equal to 123. An X2 consists
> of A, B, and C; and B must be equal to 123." This would be as precise
> as can be, but would be unnecessarily verbose and complicated, for a
> net loss in clarity. I don't see the point.
>
>> Literal equality indicates that the definition of literals should
>> rather be:
>>
>> A literal in an RDF graph consists of: - a lexical form, - a
>> datatype IRI, - and an optional language tag.
>
> No, because this definition omits the essential fact that a language
> tag is present if and only if the datatype IRI is rdf:langString.
 >
>> It would also be possible to simply include the language tag inside
>> the lexical form like this:
>>
>> A literal in an RDF graph consists of: - a lexical form being a
>> UNICODE string or a pair <UNICODE-string,BCP47-tag>, - a datatype
>> IRI.
>>
>> where only the literals with type rdf:langString can have a
>> language tag.
>
> Incorrect, because rdf:langString *must* have a language tag. And
> lacks a definition of "language-tagged string".
>
> Can you come up with better wording that is correct, complete, and
> concise?
>
> Best, Richard
>
>
>
>
>> Then equality would be defined like this:
>>
>> Literal equality: Two literals are equal if and only if the two
>> lexical forms (including possibly the language tag) and the two
>> datatype IRIs compare equal, character by character.
>>
>>
>> [1] RDF 1.1 Concepts and Abstract Syntax - W3C Editor's Draft 05
>> June 2012.
>> http://dvcs.w3.org/hg/rdf/raw-file/default/rdf-concepts/index.html
>> [2] 3.3 Literals, in [1].
>> http://dvcs.w3.org/hg/rdf/raw-file/default/rdf-concepts/index.html#section-Graph-Literal
>>
>>
-- 
>> Antoine Zimmermann ISCOD / LSTI - Institut Henri Fayol École
>> Nationale Supérieure des Mines de Saint-Étienne 158 cours Fauriel
>> 42023 Saint-Étienne Cedex 2 France Tél:+33(0)4 77 42 66 03
>> Fax:+33(0)4 77 42 66 66 http://zimmer.aprilfoolsreview.com/
>>
>
>
>


-- 
Antoine Zimmermann
ISCOD / LSTI - Institut Henri Fayol
École Nationale Supérieure des Mines de Saint-Étienne
158 cours Fauriel
42023 Saint-Étienne Cedex 2
France
Tél:+33(0)4 77 42 83 36
Fax:+33(0)4 77 42 66 66
http://zimmer.aprilfoolsreview.com/
Received on Saturday, 11 August 2012 12:46:51 UTC

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