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Re: Proposal for ISSUE-12, string literals

From: Antoine Zimmermann <antoine.zimmermann@insa-lyon.fr>
Date: Thu, 12 May 2011 12:36:15 +0200
Message-ID: <4DCBB81F.7050708@insa-lyon.fr>
To: public-rdf-wg@w3.org
The XSD specifications define the canonical form of xsd:boolean, 
xsd:decimal, xsd:float, xsd:double, xsd:dateTime, xsd:time, xsd:date, 
xsd:hexBinary, xsd:integer, xsd:nonPositiveInteger, xsd:negativeInteger, 
xsd:long, xsd:int, xsd:short, xsd:byte, xsd:nonNegativeInteger, 
xsd:unsignedLong, xsd:unsignedInt, xsd:unsignedShort, xsd:unsignedByte, 
xsd:positiveInteger.

RDF could simply rely on these definitions.

Le 12/05/2011 12:19, Richard Cyganiak a écrit :
> On 12 May 2011, at 09:22, Ivan Herman wrote:
>> - You make the remark on the wiki page on 'extending this to
>> numeric literals', which I would rather say 'extending this to any
>> datatype' (eg, xsd:dateTime, too).
>
> Right -- I changed the section heading on the wiki.
>
>> I have the impression that this is also a consequence of what you
>> write already. You emphasize the 'lexical equality', and you also
>> say "Implementations MAY replace any literal with a canonical form
>> if both are syntactically different, but have the same value."
>> which does not look like being bound to string literals.
>
> The way I wrote it, the only literals marked as canonical forms are
> plain string literals. So the sentence doesn't license replacement
> of, say, +00013 with 13, because no numeric literals have been marked
> as canonical forms. That could be easily changed, of course.
>
>> Do you think there is anything missing in this document to make
>> that picture complete (except, editorially, to possibly add
>> non-string examples)?
>
> If we only want to address string literals, then I think the proposal
> is complete.
>
> If we want to address other XSD literals as well, then some bullet
> points should be added to the list of equalities, and the canonical
> lexical form of some XSD datatypes (e.g., "13.0"^^xsd:decimal) should
> be defined to be canonical forms so that other same-valued literals
> can be replaced with the canonical form. This requires a detailed
> reading of the XSD spec (which I have not done so far).
>
> (RDF Concepts should probably contain a paragraph or two introducing
> the rdf:PlainLiteral datatype and referencing the relevant spec, but
> let's treat that as a separate issue.)
>
>> - I would also propose to make some tiny changes in the Semantics
>> document.
>
> I'll let the editors of that document comment.
>
> Best, Richard
>
>
>>
>> Ivan
>>
>>
>> On May 11, 2011, at 23:23 , Richard Cyganiak wrote:
>>
>>> I took an action today to draft text for RDF Concepts that
>>> resolves ISSUE-12. I put it on the wiki here:
>>> http://www.w3.org/2011/rdf-wg/wiki/StringLiterals/EntailmentProposal
>>>
>>>
A plain text copy is attached below.
>>>
>>> Best, Richard
>>>
>>>
>>>
>>> SHORT SUMMARY
>>>
>>> 1. RDF Concepts puts more emphasis on the distinction between
>>> (syntactic) “literal equality” and (semantic, important for
>>> applications) “value equality” 2. RDF Concepts explicitly points
>>> out the specific string value equalities that already arise from
>>> RDF Semantics 3. RDF Concepts declares one of the string literal
>>> forms as canonical 4. Implementations MAY canonicalize, but don't
>>> have to 5. The canonical form is plain literals.
>>>
>>>
>>> WHY?
>>>
>>> 1. No changes to the abstract syntax required 2. No changes to
>>> any concrete syntax or parser required 3. No changes to any
>>> implementations of any of the existing entailment regimes
>>> required 4. Those who are ok with canonicalization can do that,
>>> and don't need to deal with entailment 5. Those who don't want to
>>> canonicalize, have the option of supporting only string value
>>> equality at query time, without RDFS- and D-Entailment 6. “MAY
>>> canonicalize” softly discourages the use of xsd:string typed
>>> literals, without abolishing them outright or declaring them
>>> archaic 7. Standardizing on xsd:string was never an option
>>> because of language tags 8. Standardizing on rdf:PlainLiteral was
>>> never an option because it MUST NOT be used in serializations
>>> that support plain literals
>>>
>>>
>>> CHANGES TO 6.5.2 The Value Corresponding to a Typed Literal
>>> http://www.w3.org/TR/rdf-concepts/#section-Literal-Value
>>>
>>>
>>> §1 Rename it to “6.5.1 The Value Corresponding to a Literal” and
>>> move it ahead of 6.5.1
>>>
>>> §2 Add to the beginning: “The value of a plain literal without
>>> language tag is the same Unicode string as its lexical form.
>>>
>>> The value of a plain literal with language tag is a pair
>>> consisting of 1. the same Unicode string as its lexical form, and
>>> 2. its language tag.
>>>
>>> For typed literals, …” (continue with rest of section as is)
>>>
>>> §3 Remove the Note at the end of the section
>>>
>>>
>>> CHANGES TO 6.5.1 Literal Equality
>>> http://www.w3.org/TR/rdf-concepts/#section-Literal-Equality
>>>
>>>
>>> §4 Rename section to “6.5.2 Literal Equality and Canonical
>>> Forms”
>>>
>>> §5 Add to the beginning: “Equality of literals can be evaluated
>>> based on their syntax, or based on their value.”
>>>
>>> §6 Change “Two literals are equal …” to: “Two literals are
>>> syntactically equal …” in the current first paragraph.
>>>
>>> §7 Add to the end: “In application contexts, comparing the values
>>> of literals (see section 6.5.1) is usually more helpful than
>>> comparing their syntactic forms. Literals with different lexical
>>> forms and with different datatypes can have the same value. In
>>> particular:
>>>
>>> - A plain literal with lexical form aaa and no language tag has
>>> the same value as a typed literal with lexical form aaa and
>>> datatype IRI xsd:string - A plain literal with lexical form aaa
>>> and no language tag has the same value as a typed literal with
>>> lexical form aaa@ and datatype IRI rdf:PlainLiteral - A plain
>>> literal with lexical form aaa and language tag xx has the same
>>> value as a typed literal with lexical form aaa@xx and datatype
>>> IRI rdf:PlainLiteral”
>>>
>>> §8 “Some literals are canonical forms. Implementations MAY
>>> replace any literal with a canonical form if both are
>>> syntactically different, but have the same value. All plain
>>> literals, with or without language tag, are canonical forms.”
>>>
>>>
>>> CHANGES TO 6.3 Graph Equivalence
>>> http://www.w3.org/TR/rdf-concepts/#section-graph-equality
>>>
>>>
>>> §9 Append this leftover sentence, which was removed from 6.5.1:
>>> “Note: For comparing RDF Graphs, semantic notions of entailment
>>> (see [RDF-SEMANTICS]) are usually more helpful than the syntactic
>>> equivalence defined here.”
>>>
>>>
>>> EXTENDING THIS TO NUMERIC LITERALS???
>>>
>>> (While we're at it, we might also cover equalities between the
>>> built-in numeric XSD types, and between different lexical forms
>>> of the same built-in XSD datatype.)
>>
>>
>> ---- Ivan Herman, W3C Semantic Web Activity Lead Home:
>> http://www.w3.org/People/Ivan/ mobile: +31-641044153 PGP Key:
>> http://www.ivan-herman.net/pgpkey.html FOAF:
>> http://www.ivan-herman.net/foaf.rdf
>>
>>
>>
>>
>>
>>
>
>


-- 
Antoine Zimmermann
Researcher at:
Laboratoire d'InfoRmatique en Image et Systèmes d'information
Database Group
7 Avenue Jean Capelle
69621 Villeurbanne Cedex
France
Tel: +33(0)4 72 43 61 74 - Fax: +33(0)4 72 43 87 13
Lecturer at:
Institut National des Sciences Appliquées de Lyon
20 Avenue Albert Einstein
69621 Villeurbanne Cedex
France
antoine.zimmermann@insa-lyon.fr
http://zimmer.aprilfoolsreview.com/
Received on Thursday, 12 May 2011 10:37:24 GMT

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