CCAT: TIME: All is well
fritz@rodin.wustl.edu (Fritz Lehmann)
Date: Wed, 9 Nov 94 08:39:59 CST
From: fritz@rodin.wustl.edu (Fritz Lehmann)
Message-id: <9411091439.AA26701@rodin.wustl.edu>
To: cg@cs.umn.edu, srkb@cs.umbc.edu
Subject: CCAT: TIME: All is well
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Bernard Moulin wrote two long and thoughtful messages on time and
temporally qualified contexts (including compound tenses).
---------QUOTE BERNARD MOULIN--------
First I would like to mention that it seems strange to ask different groups
to work on separate topics like "situations", "event-process,state",
"time". From a natural language point of view all these notions are
related. You can think of a situation as supertype of event, process and
state, and all these situations involve a notion of time.
-------end quote---------
Yes I agree, these subjects are tightly interrelated and a practical
solution will treat them all. We set up the CCAT "subgroups" only to show
the scope of the CCAT core ontologies, and to allow people to indicate the
focus of their interest. I suspect the dependencies among the core
ontologies will be something like the following (in the "presupposition
order"):
ABSTRACT ALGEBRA & MATH OBJECTS "DEEP" ASSUMPTIONS
(intervals, graphs, topology etc.) (difference, something exists, etc.)
\ /
\ /
\ /
{TIME,SPACE}
/ | \
/ | motion
/ | | \
(incl. occupation PART-WHOLE | | \ (beware: counterfactual
of region \ \ | | CAUSALITY quagmire)
by substance) \ \ | | / |
\ SITUATIONS PROCESS |
\ \ / |
\ OBJECT/EVENT |
\ / REPRESENTATION (semiotic triads)
\ / /
\/ /
/\ /
/ MEASUREMENT/UNITS
/
DEEP CASE RELATIONS (between event & participants)
This is very tentative. The non-core subjects will depend on all of these.
I'd like to see a preliminary draft of Pat Hayes' TIME ontology as soon as
possible. Since it includes a notion of clocks, it may span several of the
above core subjects.
Bernard Moulin also indicated a need for a "Lap" - a specified gap or
time between intervals, expressed in seconds, days etc., as well well as a
REPEAT for iterativity (repetitive situations), NEVER and ALWAYS. I'm
confident that these can be provided by the TIME ontology. As Daniel Bobrow
pointed out, many of these notions, like "every third tuesday in 1962" can be
defined on formal discrete math objects to which times correspond, rather
than directly on time itself. Once we have some sort of time-line, the
apparatus of sets and intervals can be used (real, rational or discrete,
depending on choice of time-line). As Bobrow said, "we need a theory of
selection from ordered sets, and notions of exceptions."
Pat Hayes answered Bobrow:
-------begin HAYES quote-----
For example, the
thirteen simple-interval relations which James Allen described form a
complete algebra, and this algebraic perspective turns out to be a useful
and productive way to think about them. Suppose we allow intermittent
intervals: is there a collection of relations on them which has the same
kind of role that the Allen relations plays for simple intervals, ie is
there a useful algebra of relations-between-intermittent-intervals? People
have looked at this but I dont know of a definite answer. The questions go
beyond whether we *can* describe this stuff (answer, yes) to whether it
repays further effort to see if it can be described in other ways. And the
answer to THAT question, in my view, is whether the results from it (ie the
'theory' of intermittent intervals) are likely to be of any use to anyone.
------end quote-------
The answer is: you certainly can create variants of interval algebras
and interval orders in which the primitives are discontinuous, and no doubt
many a nice doctorate will be obtained from their study. For CCAT ontology
purposes, though, I don't think it "repays further effort", especially since
I am presuming that we will have the math and logic available to
painstakingly describe any particular discontinuous interval in terms of its
continuous components, particularly using the "notions of exceptions" Bobrow
mentioned.
David Whitten pointed out Cyc's ECTIs ("Easily Conceptualized Time
Intervals") which are a limited, useful set of intervals and interval
combinations. I suggest we adopt and name these in CCAT with the Cyc names
where convenient, but define them in the CCAT TIME ontology (which I suspect
will have the rationals as the default basis of the number line, right, Pat?)
with their closest approximation. This includes "points", intervals,
repeated intervals, fractions of intervals, and calendar periods like "1990",
as well as dyadic intersections, unions and differences of these (one-level
deep only, not recursively). Similarly, we should be able to closely mimic
the time notions in the ARPA Rome Planning Ontology, like
DURATION{INFINITY,EPSILON,ZERO}, DURATION-BOUNDS, TIME-POINT, DATE-OFFSET,
CALENDAR-DATE, TIME-INTERVAL, ALWAYS, DATES, etc., and use these names to
"tag" the corresponding CCAT TIME relations.
Moulin and Hayes asked where to get the ARPA Rome Planning Ontology;
the best source I know is the KRSL (Knowledge Representation Specification
Language) Manual. I have version 2.02 dated Feb. 1993, and Nancy B. Lehrer
of ISX Corporation (nlehrer@isx.com) is listed as the main contact. KRSL is
written in LOOM but I think they are going to change to KIF. I think they
have a gopher or WWW site at isx.com, but I don't remember the details. Try
exploring isx.com or write to Nancy Lehrer. For approximate time intervals,
the Rome ontology just provides tolerances for the beginning and end points
of an interval (like plus-or-minus fifteen minutes).
Pat Hayes and Bernard Moulin discussed indexicality and time. This
should not be cause for worry. Although self-reference is the trickiest
thing in philosophy, it should not be a problem for temporally qualified
contexts other than the outermost ("this") one. Part of Hans Kamp's, Sowa's
and Moulin's notion of a context is that it can be temporally qualified. I
surmise that there is some very tedious way of formalizing this in ordinary
logic coupled with a means of referring to a particular theory or conjuction
of statements (context) as an object. This doesn't cover our own "now" but
it would cover all the "thens" of contained contexts. I trust Bernard Moulin
to figure out the nested tenses, indexicalities, etc., once he is given the
strictly temporal primitives he needs.
I'm slightly troubled by the use of the precise MEETS relation as the
time primitive; it might be nicer to use a "robust" relation, one which is
unaffected by minuscule perturbations, as the primitive. I think Martin
Golumbic or somebody is studying this class of interval algebras (based on
the appropriate robust subset of Allen's time relations). Howevcer, we are
committed to including all of the relations listed in Walling Cyre's ICCS-93
paper, including MEETS. (Cyre's system includes the nonredundant time-
interval relations of Allen and of Matuszek, based on endpoint relations.)
I believe the system of contexts with temporal qualifications will
handle the differences between ISSUE TIME, VALID TIME, OUTLOOK TIME and
PROG(nosis) TIME described by Eli Goldberg for standard practice in weather
reporting and forecasting.
Yours truly, Fritz Lehmann
GRANDAI Software, 4282 Sandburg Way, Irvine, CA 92715, U.S.A.
Tel:(714)-733-0566 Fax:(714)-733-0506 fritz@rodin.wustl.edu
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