Re: CCAT: TIME: Fantasyland?/Various issues
To: Fritz Lehmann <>
        anquetil@IRO.UMontreal.CA,,,,,,,,,,,,,,,,, kivs@bgcict.bitnet,,,,,,,,,,,,,
In-reply-to: <> (message from Fritz Lehmann on Mon, 10 Oct 94 20:55:48 CDT)
Subject: Re: CCAT: TIME: Fantasyland?/Various issues
Date: Tue, 11 Oct 94 10:24:32 PDT
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Pat Hayes writes:
>> 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?

>      It is something that a general-purpose time system should be able
> to say.  Again, that doesn't mean we have to define this case, but the
> language should allow defining it.  I suspect that "intermittent
> intervals" can just be put together from unbroken intervals using
> negation for OFF periods and conjoining interval assertions.  Right?  No
> need to provide arbitrary algebraic interval structures, prime
> intervals, Cantor Dust, etc.

I suspect you'll want some tools for expressing recurrent events that are
capable of expressing common concepts in an elegant way.  They may or may
not have to be primitive, but they will have to be expressive.

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.

Don Dwiggins			"Things should be made as simple as possible,
Mark V Systems, Inc.		   but no simpler"                       -- Albert Einstein