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Re: RDF's curious literals

From: Story Henry <henry.story@bblfish.net>
Date: Wed, 1 Aug 2007 19:20:28 +0200
Message-Id: <F1722125-F021-4FC6-8004-4E3170E53AA3@bblfish.net>
Cc: Jeremy Carroll <jjc@hpl.hp.com>, Tim Berners-Lee <timbl@w3.org>, Semantic Web <semantic-web@w3.org>
To: Garret Wilson <garret@globalmentor.com>


On 1 Aug 2007, at 18:58, Garret Wilson wrote:
> Hi, Henry. Thanks for the discussion as well. I'm going to give a  
> couple of responses, and then rest awhile by going back to the work  
> I've been meaning to start an hour or two ago. ;)
>
> Story Henry wrote:
>> 1. you say why not "George Bush"^^xxx:president, and so why is not  
>> everything a Literal?
>>
>>    there are in fact limitations on what can be a Literal.
>
> What limitations are those---I don't remember seeing this in the  
> RDF specifications? Could "George  W. Bush"^^xxx:president be a  
> literal, if I specify the range of allow lexical forms? What cannot  
> be an instance of rdfs:Literal?

I think there is more info here:
http://www.w3.org/TR/swbp-xsch-datatypes/

The intuition I pointed out was that if you have things were the name  
of the thing can tell you everything you need to know about it, then  
you have something that is a candidate for being a Literal.


>> 2. what is the use of "123"^^xsd:integer over <http://number.eg/123>
>>
>>     Because of the Open World assumption we accept that things can  
>> have a number of names. So it is difficult to tell when two things  
>> are or are not different. For example is
>>
>>      <http://presidents.com/Bush/George> referring to the same  
>> thing <http://presidents.com/Bush/George/W> is? Well you can't  
>> tell. You may assume they are different until told otherwise
> ...
>> No need for the infinite number of statements
>>
>>      <http://numbers.eg/123> owl:differentFrom <http://numbers.eg/ 
>> 124> .
>>
>>     The same is with "hello" and "bye": they are different strings  
>> just by looking at them. If we use URLs for each string, it  
>> becomes a lot more difficult to tell them apart. So you can see  
>> that it is useful to have a distinction here.
>
> I'm sorry, but I still don't understand. You're saying that if I  
> have the URIs <http://numbers.eg/123> and <http://numbers.eg/124> I  
> don't know whether these are referring to the same resource or not,  
> even though the URIs are distinct. But if I have literals, I know  
> that the literal "123"^^xsd:integer is different from the literal  
> "124"^^xsd:integer just because they are literals. Is that what  
> you're saying?

yes. Unless of course the RDF people had decided that numbers should  
be uris starting with "http://numbers.eg/" which they could have  
done. But people would not have found it natural and you have said -  
have you not? - that it was good if languages felt natural. Why go  
against the grain? Is that not one reason you were wanting to work on  
RDFON?


> So are you saying that I also know that the literal  
> "+123"^^xsd:integer is different from the literal  
> "123"^^xsd:integer because I can simply compare the strings and see  
> that they are not equal?

No look at

http://www.w3.org/TR/swbp-xsch-datatypes/

to find out how the definitions work.  What is sure is that you don't  
need anything more than "+123"^^xsd:integer to know what you are  
speaking of. The objects can be completely specified there in the  
name. And there are an infinite number of such objects.
Received on Wednesday, 1 August 2007 17:35:45 GMT

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