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Re: RDF's curious literals

From: Story Henry <henry.story@bblfish.net>
Date: Thu, 2 Aug 2007 20:02:24 +0200
Message-Id: <D30F353A-CC29-4EF0-8C74-FC30CD1E5317@bblfish.net>
Cc: Lee Feigenbaum <lee@thefigtrees.net>, Richard Cyganiak <richard@cyganiak.de>, Garret Wilson <garret@globalmentor.com>, Tim Berners-Lee <timbl@w3.org>, Semantic Web <semantic-web@w3.org>
To: "Sandro Hawke" <sandro@w3.org>


On 2 Aug 2007, at 19:32, Sandro Hawke wrote:
> Story Henry <henry.story@bblfish.net> writes:
>
>>> Therefore, X is a datatype if and only if X is an
>>> owl:FunctionalProperty
>>> and the rdfs:domain of X contains only Unicode strings.
>>
>> well I was proposing in addition that it be a necessary truth, ie it
>> necessarily identify the thing that way,  which will bring up some
>> fun problems, but I think that the intuition behind datatypes is
>> something along those lines.
> ...
>>>> This can only work
>>>> of course if all the information is contained in the String, ie,
>>>> there is not more information to be got from anywhere else, or else
>>>> there would be no way to create a decision procedure for it. So
>>>> "George Bush"^^xxx:presidents would not work. For one, George Bush
>>>> may never have been president.
>>>
>>> But it's easy for me to construct the mapping you quoted above.   
>>> So I
>>> can't understand what you mean.  A datatype like eg:uspresidents  
>>> makes
>>> every bit as much sense as a datatype like xs:date.
>>
>> That would not work with eg:uspresidents, because Bush could have had
>> a different name, and  could also not have been president.
>>
>> With numbers on the other hand it is different. Even though 10 could
>> be written differently than "10"
>>
>> 10 xsd:int "10".
>>
>> is necessarily true.
>
> So you're saying the distinction is that datatype lexical  
> representation
> strings are rigid designators [1] ?  Hmmm.  Let me think this
> through....
>

Oh dear :-/
I did say this would bring up some fun problems....

> Again, I'll return to my example of dates, rather than integers, since
> their being socially constructed is more obvious.  There was an  
> instant
> where I paused, in writing this sentence, to record the time.  That
> instant is named in RDF as "2007-08-02T17:14:39"^^xs:dateTime.  Is  
> that
> a rigid designator?  In a world where the Gregorian calendar  
> corrections
> were never adopted, that instant would be named something more like
> ``"2007-08-16T17:14:39"^^xs:dateTime''.  (etc, etc, with all the
> different ways we could do calendars and clocks.)

ok so let me bite on the rigid designator. Of course the rigid  
designator here
is xs:dateTime. It refers rigidly to a mathematical function that is  
implemented by say
java.util.GregorianCalendar [2]. The string, being a string, rigidly  
refers to itself.

So we have a mathematical function from strings to unix time, seconds  
since 1970, which
can then be mapped to seconds since the beginning of the universe,  
which is just an index
in space time.

I think that solves your problem below.

> I think I would argue that URIs are rigid designators, so the example
> above fails because I used "xs:dateTime" to name a different mapping.
> In the first case it's the Gregorian calendar dateTime; in the second
> it's some pseudo-Julian calendar dateTime.  But the string itself,
> "2007-08-16T17:14:39" is meaningless/useless without being paired like
> that.    It's not the rigid designator itself.
>
> Similarly, my term eg:uspresidents rigidly designates the pairs of  
> names
> and presidents in my world.   So, yes, "George W.  
> Bush"^^eg:uspresidents
> is a rigid designator -- it necessarily refers to the current  
> president
> of the US in my world.

Now if we look here at the eg:uspresidents then I think it would be  
impossible to build such a
function in code that would only require the input from the string to  
get its value. Well the code
would have to have a database of all the name of presidents for it to  
work. And what if we have two presidents with the same name?

You are speaking of the subject here as rigidly designating Bush. And  
that may be. But I was thinking that the class of literals as being  
those things that can be designated by a rigidly designated  
transformation from a string.

It does seem like a slipery position to have.

:-)

>
> Isn't that right?
>
>    -- Sandro
>
> [1] http://en.wikipedia.org/wiki/Rigid_designator
[2] http://java.sun.com/j2se/1.4.2/docs/api/java/util/ 
GregorianCalendar.html
Received on Thursday, 2 August 2007 18:02:51 GMT

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