Re: CCAT: TIME and STATE
phayes@cs.uiuc.edu (Pat Hayes)
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Date: Tue, 4 Oct 1994 11:27:43 -0600
To: fritz@rodin.wustl.edu (Fritz Lehmann), srkb@cs.umbc.edu
From: phayes@cs.uiuc.edu (Pat Hayes)
Subject: Re: CCAT: TIME and STATE
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At 8:54 AM 10/4/94 -0500, Fritz Lehmann wrote:
.....
>That would be most useful. What do people expect a time reasoner to be able
>to think about? Please send me lists of concepts, if necessary with brief
>intuitive explanations of what they mean, thanks.
>-----end quote-----
>
>.......
>
> I have some immediate suggestions. Let's demand at least..
........
>
> Pat, can your three time ontologies handle all of the above?
>Can they bear the strain?
>
Of course not. This is several major research programs you have so casually
outlined here. I havent yet seen a satisfactory account of imprecision and
tolerance, for a start, including a few of my own. And "everything required
by natural language"?? Isnt that just everything?
Be a little more realistic, Fritz, or we are all in fantasyland from the
very beginning. I wanted actual concepts. For example, is the idea of an
intermittent interval ("every wednesday afteroon for the next five weeks")
a very important one for people?
For the record, my theory (actually a collection of alternative theories)
can (like many others) handle standard timedurations of various kinds and
describe clocks and calendars with various corrections, including regular
corrections like leap days. It can handle notions of faster or slower, and
what I call 'compound clocks', ie clocks which simultaneously measure time
on several scales. All binary relations between intervals in linear time,
including Allen's six, are definable. It supports several different notions
of timepoint and timeinterval and the relationships between them, and also
can describe things I call 'moments' which are pointlike intervals. Time
can be dense or discrete or any sensible combination, and it can branch or
not (usually not). So far I havnt described geographical variation as in
things like 'GMT', although that would be easy given some other
axiomatisation of the notion of location. Sidereal time might be a little
trickier, but I bet it could be arranged.
I havnt thought about relativistic time, and the theory, like any logical
axiomatisation, cannot handle indexicals. (The only indexical in KIF means
'this database', which isnt sufficient to allow temporal change.)
Question:
Is it really important to be able to represent the conceptual framework
behind these ideas, or is it sufficient to represent simply the ideas? Must
a temporal reasoner know relativity theory, for example?
Pat
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