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Re: Explicit RDF property for "literal has datatype D"?

From: Jiří Procházka <ojirio@gmail.com>
Date: Mon, 04 Jan 2010 17:32:48 +0100
Message-ID: <4B421830.9090003@gmail.com>
To: Pat Hayes <phayes@ihmc.us>
CC: Dave Reynolds <dave.e.reynolds@googlemail.com>, Semantic Web <semantic-web@w3.org>
I want to be able to express same things in RDF systems which doesn't
support literal types and language tags as in the one which does. That
means simulating those with plain literal using some extra triples in a
backwards compatible way. Is it even possible?

From what have you said I think I was talking about literal values all
the time, and I guess literal is general concept of assigning a value to
a resource, is it?

On 01/04/2010 04:06 PM, Pat Hayes wrote:
> Jiri, greetings.
> 
> You have to ask yourself, are you wanting to talk about the literals
> themselves, or about what the literals denote or refer to, ie literal
> values. The elements of rdfs:Literal are literal values, not literals.
> By and large, RDF (and OWL for that matter) *uses* literals to *refer
> to* literal values. There is no direct provision in any of these
> languages for talking about literals themselves, any more than the use
> of URIs means that you are talking about URIs themselves.
> 
> On Jan 4, 2010, at 7:58 AM, Jiří Procházka wrote:
> 
>> Hmm I guess you are right
>> (http://www.w3.org/TR/rdf-concepts/#section-Literal-Equality).
> 
> That citation refers to syntactic identity of actual literals, not to
> literal values. It is quite possible for two different literals to refer
> to the same literal value (and hence to be owl:sameAs one another.) For
> example, "abc" and "abc"^^xsd:string.

Could the same be said about "12" and "12"^^xsd:integer?
Literal value is just the character sequence, or it also contains the
type information?

This is especially hard for me to understand, since I am not a logician
and I wasn't able to decipher the RDF Semantics document, sorry :)

Best,
Jiri

> 
>> I guess some property would have to be created:
>>
>> _:x rdf:type xsd:date .
>> _:x todo:value "2008-01-01" .
>>
>> todo:value rdfs:domain rdfs:Literal . # well, typed literal, no such
>>                     class exists (yet)
>> todo:value rdfs:range rdfs:Literal . # well, plain literal :)
> 
> These would be very odd classes, if (like rdfs:Literal) they are classes
> of literal values. Since "anystring"^^xsd:string is the same value as
> "anystring", the plain literal class would be a subclass of the typed
> literal class. (See why its important to not confuse use with mention?)
> In fact, it gets worse, since its also quite possible for a blank node
> (as you yourself show) or even a URI to denote a literal value. I can
> quite legitimately write
> 
> ex:foo owl:sameAs "abc"^^xsd:string .
> 
> for example. If you base classes on what syntactic form is used to
> denote something, what class will you put this in?
> 
> Pat Hayes
> 
>>
>> that should be equivalent to saying:
>>
>> _:x owl:sameAs "2008-01-01"^^xsd:date .
>>
>> Best,
>> Jiri
>>
>> On 01/04/2010 09:28 AM, Dave Reynolds wrote:
>>> Jiří Procházka wrote:
>>>> Sorry for resurrecting this old thread, but I just stumbled upon this:
>>>>
>>>> "rdfs:Datatype is both an instance of and a subclass of rdfs:Class.
>>>> Each
>>>> instance of rdfs:Datatype is a subclass of rdfs:Literal."
>>>>
>>>> "A typed literal is an instance of a datatype class."
>>>>
>>>> citing http://www.w3.org/TR/rdf-schema/#ch_datatype
>>>>
>>>> So I think this is valid:
>>>>
>>>> _:x rdf:type xsd:date .
>>>> _:x owl:sameAs "2008-01-01" .
>>>
>>> Not as such, did you mean:
>>>
>>> _:x rdf:type xsd:date .
>>> _:x owl:sameAs "2008-01-01"^^xsd:date .
>>>
>>> ? Which would, I believe, be valid.
>>>
>>> Dave
>>>
>>>>
>>>> Quite confusing, but might be useful for RDF systems which treat
>>>> literals as just one "type" (type from their point of view).
>>>>
>>>> Shame there is no such thing for language tags, or is there?
>>>>
>>>> Best,
>>>> Jiri Prochazka
>>>>
>>>> On 07/06/2009 07:43 PM, Jeremy Carroll wrote:
>>>>> Pat Hayes wrote:
>>>>>>>> p a rdf:Property ;
>>>>>>>> rdfs:domain rdfs:Literal ;
>>>>>>>> rdfs:range rdfs:Datatype .
>>>>>>
>>>>>> _:x p xsd:date .
>>>>>> _:x :seenAsLiteral  "2008-01-01" .
>>>>> I tend to write these examples as
>>>>>
>>>>> _:x p xsd:date .
>>>>> _:x owl:sameAs  "2008-01-01" .
>>>>>
>>>>> Semantically that has a literal as the subject, and it works around
>>>>> the
>>>>> legacy syntactic restriction
>>>>>
>>>>> Unfortunately the reasoning required to make this work means that
>>>>> simple
>>>>> RDF systems may well not get it.
>>>>>
>>>>> Jeremy
>>>>>
>>>>>
>>>>>
>>>>
>>>
>>
> 
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Received on Monday, 4 January 2010 16:33:28 UTC

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