Re: CCAT: TIME: Fantasyland?/Various issues

Danny Bobrow <bobrow@parc.xerox.com>
Message-id: <8iczDMIB0V0w43Mk0x@nero.parc.xerox.com>
Date: 	Tue, 18 Oct 1994 09:12:08 PDT
From: Danny Bobrow <bobrow@parc.xerox.com>
To: dwig@markv.com, Fritz Lehmann <fritz@rodin.wustl.edu>,
        phayes@cs.uiuc.edu (Pat Hayes)
Subject: Re: CCAT: TIME: Fantasyland?/Various issues
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It seems that the concepts  such as every last Friday of every third
month are not concepts of time, but concepts that derive from our
ability to count, select and name. I can ask for every tallest student
from every third classroom, etc.  Once we have chunks, and names for
chunks of time (MTWHFSS, or Jan Feb, or 1884) and an ordering among
names, then we can use our ability to compose selection functions on
ordered sets   The fact that some calendar programs select some of these
is "just" user convenience (no small matter if you want to sell).  So we
need a theory of selection from ordered sets, and notions of exceptions.

Or am I missing something deep?

danny
Excerpts from mail: 17-Oct-94 Re: CCAT: TIME: Fantasyland.. Pat
Hayes@cs.uiuc.edu (1325*)


> >To Pat's call for actual concepts, here are some recurrences my personal
> >organizer tool (Ecco, from Arabesque software) supports: "every Tuesday",
> >"2nd Tuesday of every month", "11th of every month", "every Oct. 11th",
> >"every Nth Tuesday", "last business day of every month".  Also, in place of
> >"every month" you can specify "every Nth month".
> >
> >Finally, here's the definition for the date of Easter: "the first Sunday
> >after the first full moon after the vernal equinox".  I seem to remember
> >similar definitions of Islamic dates.
> >
> Great! Thanks, thats just the kind of thing I wanted. I think these are all
> definable, but it will take work.

> Hres a further question. What kind of relations between these concepts are
> important? For example, the 12th of every month follows, in a sense, the
> 11th of every month. Is this significant? Or do you just want to be able to
> keep track of particular dates and times?

> pat


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