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Re: RDF 1.1 Semantics: LV and typo

From: Peter F. Patel-Schneider <Peter.Patel-Schneider@nuance.com>
Date: Wed, 24 Sep 2014 17:08:43 -0700
Message-ID: <54235D0B.8060300@nuance.com>
To: Aidan Hogan <aidhog@gmail.com>
CC: "<public-rdf-comments@w3.org>" <public-rdf-comments@w3.org>


On 09/24/2014 04:48 PM, Aidan Hogan wrote:
> Thanks for the quick response! Comments in line.
>
> On 24/09/2014 19:58, Patel-Schneider, Peter wrote:
>> Hi:
>>
>> This is an unofficial reply.
>>
>> LV is mostly around in the 1.1 semantics to provide a link back to the LV in
>> the older semantics.  It could be removed without any trouble.
>>
>> However, LV is not defined circularly.  LV is defined in terms of ICEXT, I,
>> and rdfs:Literal.
>>
>> ICEXT is defined just above, and that definition uses IEXT, I and rdf:type.
>>
>> IEXT is part of every interpretation.
>>
>> I is defined in the semantic conditions for ground graphs.  For IRIs, I is
>> defined in terms of IS, which is part of every interpretation.
>>
>> So, no circularity.
>
> To clarify, the unknown quantity on the right hand side for me is
> rdfs:Literal. The class extension of rdfs:Literal has not been previously
> defined / mentioned up to that point.

rdfs:Literal (actually http://...whatever..../Literal) is an IRI, which exists 
independently of interpretations.

> Hence it seems to me that LV (which is
> not defined up to that point) and the extension of rdfs:Literal (which is not
> defined up to that point) are both unknown quantities. (My expectation was
> that rdfs:Literal would be defined in the semantic conditions in a similar way
> to, say, rdf:Property.)
>
>> Defining LV as you suggest would have some interesting consequences.   You
>> would be able to reason that a literal value (an arbitrary element of LV) is
>> one of the literals that you can enter.  I don't think that you can conclude
>> anything from this in RDF, but in OWL you can.
>
> Understood. I see now that in D you could have a datatype without concrete
> lexical strings for some values (e.g., owl:real?) and with this definition,
> those values would not be a rdfs:Literal, thus causing problems saying that,
> e.g., every datatype is a subclass of literal. (The key realisation for me
> here is that L2V is not necessarily "surjective".)
>
> In this case, I guess like the notion of rdfs:Class, the notion of
> rdfs:Literal is "new" in a sense and cannot be (easily) "derived".
>
>> You should think of IC and IV simply as shorthands.  They can be replaced
>> everywhere in the current semantics by their definitions,
>> ICEXT(I(rdfs:Class)) and ICEXT(I(rdfs:Literal), respectively.
>
> Understood.
>
>>
>> peter
>>
>>
Received on Thursday, 25 September 2014 00:09:16 UTC

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