- From: Pat Hayes <phayes@ihmc.us>
- Date: Thu, 12 Dec 2013 01:28:17 -0800
- To: Markus Lanthaler <markus.lanthaler@gmx.net>
- Cc: Thomas Baker <tom@tombaker.org>, RDF Working Group <public-rdf-wg@w3.org>
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. 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 ------------------------------------------------------------ IHMC (850)434 8903 home 40 South Alcaniz St. (850)202 4416 office Pensacola (850)202 4440 fax FL 32502 (850)291 0667 mobile (preferred) phayes@ihmc.us http://www.ihmc.us/users/phayes
Received on Thursday, 12 December 2013 09:28:47 UTC