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Re: Plain literals in Canonical N-triples

From: Andy Seaborne <andy@apache.org>
Date: Sun, 28 Dec 2014 11:40:47 +0000
Message-ID: <549FEC3F.1050707@apache.org>
To: public-rdf-comments@w3.org
On 28/12/14 05:04, Pat Hayes wrote:
>
> On Dec 27, 2014, at 9:24 PM, Stian Soiland-Reyes <soiland-reyes@cs.manchester.ac.uk> wrote:
>
>> No, for once I am not coming from OWL :)
>>
>> I'm just writing a simple n-triples serializer, and I am not sure if I should simply always include the type if there is no @lang (e.g. ^^xsd:string)
>
> It was certainly the intention of the RDF 1.1 WG that every literal should have a type. We even provided a special 'type' for the @lang case, to preserve this intention. It seems to me that one should not ever go wrong by including the ^^xsd:string, which was semantically correct even in original RDF, whereas really plain plain literals now have the shadow of deprecation hanging over them, at the very least.
>
> Hope this helps.
>
> Pat Hayes

And for serialization, the WG intention IIRC was that all ^^xsd:strings 
should be written without the ^^xsd:string in all formats where 
possible.  It look nicer.

http://www.w3.org/TR/rdf11-concepts/#section-Graph-Literal only says 
"MAY" -- that is mainly so as not to suggest much RDF 1.0 data output by 
pre-existing software is suddenly invalidated, which it isn't.

	Andy


>
>> ..Or if I should have a special case to output anything with type xsd:string as a classic "plain literal", e.g. no @ or ^^.
>>
>> Surely just one of these should be in the canonical version ? My guts says to always include the type for non-lang, but the spec is ambigous on this - if xsd:string is implied, should I then prefer to generate this implied version?
>>
>> Before rdf 1.1 the norm tended to be to NOT express xsd:string unless it really was a character-by-character string (e.g. a genome identifier), and not when it was human text (but in unknown or mixed language).
>>
>> As we SHOULD be generating the Canonical N-Triples, then it would be good to know if there already is a silent de facto agreement that is just not expressed in the spec.
>>
>> You might know the code base -
>> https://github.com/stain/commons-rdf/blob/tests/src/test/java/com/github/commonsrdf/dummyimpl/LiteralImpl.java#L99
>>
>> On 27 Dec 2014 17:14, "Peter Ansell" <ansell.peter@gmail.com> wrote:
>> Hi Stian,
>>
>> RDF-1.1 does not have the concept of plain literals [1]. Hence, it is
>> difficult to map the OWL-WG-derived rdf:PlainLiteral set to RDF-1.1,
>> if that is where you are coming at the issue from [2].
>>
>> Cheers,
>>
>> Peter
>>
>> [1] http://www.w3.org/TR/2014/REC-rdf11-concepts-20140225/#section-Graph-Literal
>> [2] https://github.com/owlcs/owlapi/issues/172
>>
>> On 27 December 2014 at 16:37, Stian Soiland-Reyes
>> <soiland-reyes@cs.manchester.ac.uk> wrote:
>>> In http://www.w3.org/TR/n-triples/#canonical-ntriples I read:
>>>
>>>> Canonical N-Triples has the following additional constraints on layout:
>>>>
>>>>      The whitespace following subject, predicate, and object MUST be a single space, (U+0020). All other locations that allow whitespace MUST be empty.
>>>>      There MUST be no comments.
>>>>      HEX MUST use only uppercase letters ([A-F]).
>>>>      Characters MUST NOT be represented by UCHAR.
>>>>      Within STRING_LITERAL_QUOTE, only the characters U+0022, U+005C, U+000A, U+000D are encoded using ECHAR. ECHAR MUST NOT be used for characters that are allowed directly in STRING_LITERAL_QUOTE.
>>>
>>>
>>> and in http://www.w3.org/TR/n-triples/#sec-parsing-terms
>>>
>>>> If neither a language tag nor a datatype IRI is provided, the literal has a datatype of xsd:string.
>>>
>>>
>>> and in http://www.w3.org/TR/n-triples/#sec-literals
>>>
>>>> If there is no datatype IRI and no language tag it is a simple literal and the datatype is http://www.w3.org/2001/XMLSchema#string.
>>>
>>>> Example 3
>>>>      <http://example.org/show/218> <http://www.w3.org/2000/01/rdf-schema#label> "That Seventies Show"^^<http://www.w3.org/2001/XMLSchema#string> . # literal with XML Schema string datatype
>>>>      <http://example.org/show/218> <http://www.w3.org/2000/01/rdf-schema#label> "That Seventies Show" . # same as above
>>>
>>>
>>> So I am not any wiser with regards to how to serialize plain literals
>>> in RDF 1.1 Canoical N-Triples..
>>>
>>>
>>> Are both of the two examples allowed in Canonical N-Triples? (it seems
>>> so by the spec.. :-( ).
>>>
>>> Which variant should I generate?
>>>
>>>
>>> --
>>> Stian Soiland-Reyes, myGrid team
>>> School of Computer Science
>>> The University of Manchester
>>> http://soiland-reyes.com/stian/work/ http://orcid.org/0000-0001-9842-9718
>>>
>
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Received on Sunday, 28 December 2014 11:41:22 UTC

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