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Re: Turtle data-type

From: Henry Story <henry.story@bblfish.net>
Date: Wed, 29 May 2013 08:31:46 +0200
Cc: Kingsley Idehen <kidehen@openlinksw.com>, public-rdf-comments@w3.org
Message-Id: <85DD7AE5-7C50-4019-8A44-F250AAAC3379@bblfish.net>
To: Peter Ansell <ansell.peter@gmail.com>

On 29 May 2013, at 07:38, Peter Ansell <ansell.peter@gmail.com> wrote:

> On 29 May 2013 15:29, Henry Story <henry.story@bblfish.net> wrote:
> 
> On 28 May 2013, at 21:41, Kingsley Idehen <kidehen@openlinksw.com> wrote:
> 
> > On 5/20/13 11:39 AM, Henry Story wrote:
> >> In Turtle there is no way of specifying a graph (other than through reificiation which
> >> is understood to be broken).
> >
> > Why is reification assumed to be broken? I think the perception is that its cumbersome due to data bloat. Like blank nodes, this is a feature of RDF that's often misunderstood and then in the process maligned.
> >
> > Reification is the powerful mechanism for granular descriptions of triples (statements) without exiting existing RDF semantics.
> 
> It does not do quotation the way we need it.
> 
> I want to express the following:
> 
> Laura Lane believes that Superman is a Hero .
> Superman is Clark Kent .
> 
> With the suggested notation .
> 
> lane:Laura believes """@prefix ...
>    super:man a Hero .
> """^^lang:Turtle .
> super:man owl:sameAs kent:Clark .
> 
> With reification
> 
> lane:Laura believes _:b .
> _:b rdf:subject super:man ;
>     rdf:relation rdf:type ;
>     rdf:object Hero .
> super:man owl:sameAs kent:Clark .
> 
> Now since owl:sameAs allows substitution of identicals salva veritate,
> it follows from the reification example but not from the quotation example
> that Laura Lane believes that Clark Kent is a Hero.
> 
> 
> IMO, Laura Lane *would* believe that Clark Kent is a Hero if she were privileged to know the information inside of *either* the quotation or the reification. 

To be precise if:

  lane:Laura believes ".... super:man owl:sameAs kent:Clark "^^lang:Turtle 

then you could come to the conclusion that she should believe that Clark Kent is a Hero.
But that is something that may or may not be true.


> Are you trying to create an alternative for reification for use in RDF that is specifically not compatible with OWL to avoid conflicts with the OWL semantics?

Not at all. 

The Laura Lane example is just a modernization of examples that stem from Frege, and that 
have been analysed in philosophy of language and logic since the beginning of the subject.

In the semantic web this has clearly been accepted with SPARQL graphs, NQuads,
N3, .... I am just pointing out that this has been available if hidden in RDF from the
beginning. 

>  
> You can argue that is not broken because it is not the same as quotation
> and it just does something else, and that would be fine.
> 
> But we need the quotation mechanism, for many use case. It is not bringing any new
> semantics into RDF in any case: it's just asking for a notation to
> express what you can already express. We'd just like a standard notation
> for something as important as this. defining lang:Turtle as a datatype,
> with a well known w3c url.
> 
> 
> So if there are no new semantics, does that imply that the quotation has no effect unless the interpreter manually extracts the Turtle from the Literal and interprets it outside of the RDF graph derived from the document? 

Indeed. You need a further non-automatic step to extract content from a quoted context.
And more to the point you need a further step to add something to a quoted context.
If you want to come to an idea of what Laura Lane believes you need to add a statement to
her belief context. It is not because something is true that everyone believes it to be the case.

> 
> Are you able to use the existing well-known W3C URL for Turtle, http://www.w3.org/ns/formats/Turtle , and others from the list at http://www.w3.org/ns/formats/ in a similar way?

$ cwm  http://www.w3.org/ns/formats/Turtle 
     @prefix : <http://xmlns.com/foaf/0.1/> .
    @prefix dcterms: <http://purl.org/dc/terms/> .
    @prefix foa: <http://www.ivan-herman.net/foaf#> .
    @prefix formats: <./> .
    @prefix rdfs: </2000/01/rdf-schema#> .
    
    foa:me     a :Person;
         rdfs:seeAlso <http://www.ivan-herman.net/foaf>;
         :mbox <mailto:ivan@w3.org>;
         :name "Ivan Herman";
         :title "Semantic Web Activity Lead";
         :workplaceHomepage <http://www.w3.org> .
    
    formats:Turtle     a formats:Format;
         dcterms:created "2010-05-03";
         dcterms:creator foa:me;
         dcterms:description "Unique identifier for the RDF Serialization in Turtle";
         dcterms:modified "2013-03-25";
         rdfs:comment "Turtle is defined by the “Turtle - Terse RDF Triple Language” W3C Candidate Recommendation.";
         rdfs:isDefinedBy </TR/turtle/>;
         rdfs:seeAlso </TR/turtle/#sec-mediaReg>;
         formats:media_type "text/turtle";
         formats:preferred_suffix ".ttl" .

I am not entirely sure. I could not dereference http://www.w3.org/ns/formats/ 
to see if it is a datatype definition.

But if it were a Datatype definition then one could have a datatype for each of the
serialisations. It would make sense to do so. I limited myself to Turtle here as
I have a use case for it.



> 
> Peter

Social Web Architect
http://bblfish.net/
Received on Wednesday, 29 May 2013 06:32:22 UTC

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