Re: rdf semantics and timelessly true

On 14 Nov 2012, at 17:42, 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? 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?

You need to distinguish between the context free truth of RDF semantics - which is what makes it possible to have very simple graph merging algorithms, and the separate decision about whether you trust some source of information and for how long [1]

HTTP headers give you information about how long a representation is valid for so that is one thing to take into account. You may also change your mind about whome to trust.

But there is also an issue of good modelling. Relations and ontologies should I think create atemporal 
relations. I don't think many people are aware of this issue. One can always map from one to another if one has the right context - but then we have a temporal context which won't allow rdf reasoning to function correctly I think.

   https://blogs.oracle.com/bblfish/entry/temporal_relations

That means that one needs in the end notions of timeslices and mereological reasoning.


[1] https://blogs.oracle.com/bblfish/entry/beatnik_change_your_mind

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