W3C home > Mailing lists > Public > semantic-web@w3.org > November 2012

Re: rdf semantics and timelessly true

From: Pat Hayes <phayes@ihmc.us>
Date: Wed, 14 Nov 2012 09:45:06 -0800
Cc: Sergey Larionov <s.larionov@rks.karelia.ru>, Semantic Web <semantic-web@w3.org>
Message-Id: <697810D7-A391-45EE-9EC0-A41005BDCE90@ihmc.us>
To: nathan@webr3.org

On Nov 14, 2012, at 8:42 AM, Nathan 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? 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?

Its fine to coin a new URI for yourself. The issue arises if you want to re-use your old URI to refer to something different. What you *ought* to do, according to the strict RDF rules (and TimBL's idea of "cool URIs") is to coin a new URI for the new thing and keep the old one meaning the same thing as it always did. But note, it is fine for this "thing" to be something that is dynamic, ie which has states that change with time. LIke a daily newspaper, for example. But then you need to be careful to distinguish this thing from one of its states... 



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Received on Wednesday, 14 November 2012 17:45:41 UTC

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