Re: Plain literals in Canonical N-triples

On Dec 28, 2014, at 5:40 AM, Andy Seaborne <andy@apache.org> wrote:

> 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.

Really? I have no recollection of that, but I may have missed some discussions. Can you find this in the minutes or emails anywhere?

>  It look nicer.

Maybe, but it also can produce uncertainty, as for example: 

"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)."  

Even in RDF 1.0, plain literals were specified to be semantically identical to xsd:string-typed literals, but this was buried in the semantics dociument which nobody read, and because the syntactic distinction was available, people assumed it meant something. As long as a syntax offers both choices, this misreading process will continue to operate, even now RDF 1.1 has said explicitly that plain literals are only syntactic sugar for the typed version. 

> 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.

Certainly, plain literal surface syntax is not *invalidated* by RDF 1.1. Sorry if I gave that impression. 

Pat


> 
> 	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 23:31:55 UTC