- From: Pat Hayes <phayes@ihmc.us>
- Date: Wed, 11 Oct 2006 10:48:24 -0500
- To: Feng Pan <pan@ISI.EDU>
- Cc: Antoni Mylka <Antoni.Mylka@dfki.uni-kl.de>, public-swbp-wg@w3.org
>Hi Antoni, > >Thank you for your comments. > >>Many applications use the TZ timezone database >>(http://www.twinsun.com/tz/tz-link.htm). Is there a mapping between TZ >>timezones and the timezones from the www.w3.org/2006/timezone-world or >>www.w3.org/2006/timezone-us? > >No, currenly there is no mapping between them, but it would be useful >to explore that. > >>The DurationDescription class doesn't support negative durations >>(as the XSD duration datatype does). Such negatve durations come up in iCal >>files. (That's why using a DurationDescription to represent an ical Duration >>would need some additional information if it's negative) > >Thank you for pointing that out. I think the negative durations are >only used for subtractions in temporal arithmetic. For those cases, >subtraction rules can be applied to the positive durations. They do have other, more 'ontological' uses. For example, if one is reasoning about the interval by which one event precedes another - defined as the interval <start(event1), start(event2)> - it can be useful to allow a negative interval to represent the fact that event2 started earlier than event1. In general, negative intervals provide an analogous utility in temporal reasoning to that which negative numbers provide in arithmetic, in effect by making the algebra more complete and so providing more solutions to temporal constraints. They mean for example, that any two timepoints P and Q define an interval <P, Q>. Just as with negative numbers, however, the cost is that the algebra is more complicated: the Allen interval algebra applies only to positive intervals. Pat Hayes -- --------------------------------------------------------------------- IHMC (850)434 8903 or (650)494 3973 home 40 South Alcaniz St. (850)202 4416 office Pensacola (850)202 4440 fax FL 32502 (850)291 0667 cell phayesAT-SIGNihmc.us http://www.ihmc.us/users/phayes
Received on Wednesday, 11 October 2006 15:48:39 UTC