Re: RDF 1.1: "Some properties may change over time." (ISSUE-178)

On Dec 12, 2013, at 04:28, Pat Hayes <phayes@ihmc.us> wrote:

> 
> On Dec 11, 2013, at 10:34 AM, Markus Lanthaler <markus.lanthaler@gmx.net> wrote:
> 
>> On Wednesday, December 11, 2013 7:18 AM, Thomas Baker wrote:
>>> On Tue, Dec 10, 2013 at 11:29:00PM -0600, Pat Hayes wrote:
>>>>> Works for me. We could perhaps make it even simpler by just saying
>>>>> 
>>>>> A relationship that holds between two resources at one time may
>>>>> not hold at another time.
>>> 
>>> Pat's answer (below) is certainly the more interesting.  However, the
>>> simple bulleted list at [1] is not a good place to first raise such a
>>> subtle issue. If Pat's judgement amounts to weak assent, I'd vote +0.5
>>> for the "least bad" variant above.
>> 
>> OK, I went ahead and made the change. Tom, Pat, could you please tell me
>> whether you can live with this so that we can close ISSUE-178?
> 
> Yes, I can live with it.

Just so I am on record, I’m fine with this too.  Thanks, Markus, Pat and Tom.

Regards,
Dave
--
http://about.me/david_wood



> 
> Pat
> 
>> 
>> 
>> Thanks,
>> Markus
>> 
>> 
>> 
>>> [1] https://dvcs.w3.org/hg/rdf/raw-file/default/rdf-
>>> concepts/index.html#change-over-time
>>> 
>>>> This last one is the least bad of the lot. But none of them are
>>> correct.
>>>> There is a basic issue here. Just like sets, relations cannot really
>>> change
>>>> with time. At least, not when they are described using a normal logic
>>> (they
>>>> can in a tense logic). What can happen is that something that we
>>> might
>>>> casually or carelessly describe as a binary relation is in fact a
>>> three-way
>>>> relation with time as its third argument. Now of course [ R(a, b) at
>>> T ] or
>>>> R(a, b, T) pretty much mean the same thing and in English we don't
>>> even have
>>>> a way to distinguish them; but being all logical and strict about it,
>>> the
>>>> three-argument way of talking is more accurate precisely because it
>>> makes it
>>>> clear that the *actual relation* does not change, which makes sense
>>> because
>>>> relations (speaking now formally and mathematically proper), like
>>> sets, just
>>>> aren't the kind of thing that can possibly change. (If this reminds
>>> y'all of
>>>> the problems we had with talking about RDF graphs being updated or
>>> modified,
>>>> yes it is exactly the same issue.) We could have made RDF into a
>>> tensed
>>>> logic, in which all assertions are made at a time, and things like a
>>> triple
>>>> being true AT a time would make literal sense; but we didn't. So
>>> right now,
>>>> and probably for the forseeable future, the idea of a relation
>>> changing -
>>>> holding at one time but not at another time - does not make sense
>>> according
>>>> to the RDF conceptual model, so temporal variation like this has to
>>> be
>>>> modeled in the same way we would model a three-place relation in RDF.
>>>> 
>>>> We might say something like this:
>>>> 
>>>> Some relations have an extra time parameter or are time-dependent.
>>> Such a
>>>> relationship that holds between two resources at one time might not
>>> hold at
>>>> another time. To describe this in RDF we have to treat the time as an
>>> extra
>>>> argument or parameter to the binary relation.
>>> 
>>> --
>>> Tom Baker <tom@tombaker.org>
>> 
>> 
>> --
>> Markus Lanthaler
>> @markuslanthaler
> 
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