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Re: rdf semantics and timelessly true

From: Charles McCathie Nevile <chaals@yandex-team.ru>
Date: Wed, 14 Nov 2012 18:31:13 +0100
To: "Pat Hayes" <phayes@ihmc.us>, Nathan <nathan@webr3.org>
Cc: "Sergey Larionov" <s.larionov@rks.karelia.ru>, "Semantic Web" <semantic-web@w3.org>
Message-ID: <op.wnrxmbety3oazb@v3-151-181.yandex.net>
On Wed, 14 Nov 2012 17:42:41 +0100, Nathan <nathan@webr3.org> wrote:

> Pat Hayes wrote:
>> On Nov 14, 2012, at 8:03 AM, Nathan wrote:
>>
>>> Hi Pat,
>>>
>>> Pat Hayes wrote:
>>>> Its not impossible, and in a strong sense this is required by the  
>>>> current RDF semantics, which treats all RDF assertions as timelessly  
>>>> true.
>>> Can you refine / expand on this please? I'd presumed RDF to have no  
>>> consideration of time - e.g time-less; as opposed to being true for  
>>> all time (timeless).
>>>
>>> TIA,
>>>
>>> Nathan
>>  Yes, time-less is a better way to put it. But it is so because  
>> URIreferences are assumed (and I know this is an idealization, but...)  
>> to be timeless in how they refer. Section 1.2 says:  "... the semantics  
>> simply assumes that ... a single URI reference can be taken to have the  
>> same meaning wherever it occurs. Similarly, the semantics has no  
>> special provision for tracking temporal changes. It assumes,  
>> implicitly, that URI references have the same meaning whenever they  
>> occur."
>>  In other words, no counters allowed.
>
> What about any data that changes?

In the strict sense, no.

> if <http://webr3.org/nathan#me> refers to "me", and I change my name  
> from Nathan to Bob, then I cannot update my RDF to reflect this? or  
> perhaps more realistically, my email address?

Only if you use something like rules that enable you to state a  
contradiction. In the basic RDF world, if you say

My name is bob
my name
   after tuesday
   is not bob
my name is nathan

all these things are true. I.e. you need something that understands your  
rules of "after tuesday" and "is not" which goes beyond basic processors.

cheers

Chaals

-- 
Charles McCathie Nevile - Consultant (web standards) CTO Office, Yandex
       chaals@yandex-team.ru         Find more at http://yandex.com
Received on Wednesday, 14 November 2012 17:31:58 GMT

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