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Re: Comment: issues with owl time

From: Pat Hayes <phayes@ihmc.us>
Date: Wed, 11 Oct 2006 10:48:24 -0500
Message-Id: <p06230902c152c0cabdf9@[10.100.0.128]>
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
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Received on Wednesday, 11 October 2006 15:48:39 UTC

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