- 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>
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]. Tom [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