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

From: 'Thomas Baker' <tom@tombaker.org>
Date: Wed, 11 Dec 2013 14:43:50 -0500
To: Markus Lanthaler <markus.lanthaler@gmx.net>
Cc: 'Pat Hayes' <phayes@ihmc.us>, 'RDF Working Group' <public-rdf-wg@w3.org>
Message-ID: <20131211194350.GA31222@julius.local>
On Wed, Dec 11, 2013 at 07:34:36PM +0100, Markus Lanthaler 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?

I can live with this.  "Relationship" is sufficiently less specific than
"statement" or "property" that I think it unlikely to be misinterpreted.

That said, I like Pat's exposition of the issue.  It is a pity we have place to
collect this and other useful clarifications such as [1] and my personal
favorite, [2].


[1] http://www.ihmc.us/users/phayes/PatHayesAbout.html
[2] http://lists.w3.org/Archives/Public/public-rdf-wg/2012Nov/0305.html

Pat wrote:
> > 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>
Received on Wednesday, 11 December 2013 19:44:25 UTC

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