- From: pat hayes <phayes@ihmc.us>
- Date: Mon, 19 Jan 2004 12:23:47 -0600
- To: Austin Tate <a.tate@ed.ac.uk>
- Cc: public-sws-ig@w3.org
>At 05:16 PM 16/01/2004 -0600, pat hayes wrote: >>>I have argued that SWSL should simply allow a process description >>>to be made up of: >>> >>>a) a set of activities to be performed, each of which are >>>considered to have a begin and end time point >> >>Suggestion: each process occupies (? lasts for, endures during, >>takes) a time-interval, and intervals have begin and end timepoints >>(and indeed are defined by them, uniquely.) Intervals are handy >>things to have in the ontology anyway. > > >Agreed... and that is what I meant. An activity always is associated >with a time interval defined as the begin time point of the interval >and the end time point of the interval. *** > >As you know we formulated this simple description (used in NIST PSL >too) long ago along with James Allen - Mr. Interval:-) - and he has >no problem with seeing intervals as having two time point ends >(begin and end) - transformation between the two is always possible >- contrary to some early arguments that this might not be so. Yep. The key is to not require that an interval is the set of points which are 'in' it. Forcing a decision about the endpoints being 'in' or 'out' is what causes all the old problems. (Or, one can, as you say, think of the endpoints as having two 'sides' and it comes to the same thing. Bottom line: classical topology isn't a good way to think about time.) BTW, the same abstraction works very well for space. Traditional spatial models start with points (where you click the digitizing pen on the map) then go to (oriented) line-segments (pair of points) then to end-linked sequences (paths) then to closed paths (end=beginning and no crossings) which define (oriented) 2-d regions. These all build up very nicely as finite structures on points. You can even go to 3-d and higher, using ideas from homology theory, by stitching together 2-d cells into 2-d surfaces and defining closure by cancellation of oriented edges. All of which suggests that this is indeed a very robust (and certainly very simple) framework. Pat -- --------------------------------------------------------------------- IHMC (850)434 8903 or (650)494 3973 home 40 South Alcaniz St. (850)202 4416 office Pensacola (850)202 4440 fax FL 32501 (850)291 0667 cell phayes@ihmc.us http://www.ihmc.us/users/phayes
Received on Monday, 19 January 2004 13:23:48 UTC