|Vol. 2, Nr. 2||Editor: Erik Sandewall||28.2.1998|
|Commonsense workshop continues discussions online and in our Newsletter|
|Ontologies for actions and change|
The recent workshop on Formalization of Commonsense Reasoning in London on January 7-9 featured 23 presented papers, as well as two panel discussions. The discussions at the workshop were very lively and informative, and it was decided to make an experiment with pursuing the discussions online. The result is now available in the ETAI web structure, and to go there directly please use http://www.ida.liu.se/ext/etai/nj/fcs-98/listing.html
The structure rooted at that URL contains a discussion summary that the participants have a had a chance to correct and augment (although additional amendments may be forthcoming), but it is also intended as a starting point for continued discussion. Thus, the online workshop discussions will proceed in the same manner as our discussions about ETAI received papers and our existing on-line panels. Also, it is of course not restricted to workshop participants: every reader of the Newsletter is invited to take this opportunity to ask questions to the authors.
Just like in a question period in a seminar, this is for the benefit of all: if one person thought something required further explanation and asked a question, then chances are that several others will also find the question and the answer useful. In fact, this style of presentation may be an excellent way of explaining a piece work, just like a list of "Frequently Asked Questions" and their answers may be more readable than a plain text containing the same information. In other words, you are making the author a favor by asking a good question to her or him.
However, in one respect the discussion about workshop papers differs from our earlier online discussions: we don't send out the initial part by e-mail, simply because the resume of questions and answers is too voluminous. Follow-up questions and comments concerning a point that was first addressed in the discussion at the workshop will have to be understood by relating to the existing online structure (URL above).
Although many of the workshop papers addressed reasoning about actions and change, some of them concerned other aspects of commonsense reasoning. (Mutatis mutandis, there are some aspects of reasoning about actions and change that don't really qualify as formalization of commonsense). However, although the online discussion is run through the Actions and Change Newsletter and Colloquium, we'll be generous and include all the articles. This means in particular that researchers outside the constituency of the present Newsletter may also be interested in seeing the discussion and in participating. If you know someone who might be interested on that account, please forward this Newsletter to her or him.
An Action Language Based on Causal Explanation: Preliminary Report
Ramifications and sufficient causes
From: Michael Gelfond on 2.2.1998
As I see it, in the "basic" approaches to the frame problem (Reiter's
completion, Sandewall form of chronological minimization, language
If you replace
A model of
Observations not only prune "the set of possible trajectories"
but also change the actual path in each model.
This gives the nonmonotonicity of entailment in
Is this nonmonotonicity "in the set of observations"?
|In other models, Michael's and Luís' included, actions are represented in the state (in one way or the other) and hence abduction to both fluents and actions are supported. Such models are non-monotonic in the set of observations. Actually the only apparent difference in such models between actions and fluents is that the former are assumed to be "false by default" while the latter...|
You are right when you say that
From: Pat Hayes on 12.2.1998
Responses to Judea Pearl and Erik Sandewall in ENRAC 26.1 (issue 98009):
Responses to Judea (all quotations from his message 26.1):
On Actions vs Observations, or on Pat Hayes' reply to Geffner, Poole and me:
| ... the cleavage between the culture that Hector, David and I
represent and the one represented by Pat has gotten so DEEP that we
are not even sure we are talking about the same thing.
| Pat does not think the "distinction between sensing and acting is
either necessary or even ultimately coherent". For him, observing a
surprising fact evokes the same chain of reasoning as establishing
that fact by external act. In both cases, so claims Pat, the world
is changing, because a world is none other but one's beliefs about
the world, and these do change indeed in both cases.
| ... there
is no need to invoke such dramatic phrases as "changing worlds" for things
that we know how to handle by standard inference methods. (e.g., adding
a proposition "light on" to the system and let a classical theorem
prover draw the consequences. [and if our current beliefs contain
"light off" then the contradiction can be handled by either temporal
precedence or minimal-change belief-revision]).
| [we need to decide]... when a change is considered a "world-change" and
when it is merely a "belief change".
Is flicking the switch and seeing the light come on an example of
a changing world ?
| From a physical viewpoint, the world has obeyed Schrödinger's
equation before and after the action, so it has not changed at all.
One last comment:
| ... we are not dealing here with physics or psychology. We are dealing
with various formal systems for modeling the world and our beliefs
about the world.
Responses to Erik
In his message 26.1, referring to an earlier message by myself, he wrote:
| In the sitcalc (any variety), actions are changes in the world, not motor
commands. One plans by thinking about the changes, not by thinking about
the muscles one is going to use. Putting such a system into a robot
requires one to somehow connect these actions with motor controls, no
doubt, but they shouldnt be identified. (Murray and Ray, do y'all agree??)
| However, earlier in the same contribution Pat had written:
| ... Our peripheral systems often blend motor action and lowlevel perception
in tight feedback control loops, so that our bodies seem to 'move by
themselves', but these lowlevel controls are the result of more cognitive
decision-making (deciding to hit a tennis ball, say.)
| Pat, I can't make sense out of your position: at one point you seem to
argue that low-level and high-level descriptions of actions can't ever
be separated; at another point you seem to say that they are best
treated in complete separation.
| My own preference is to take both into account, but to be precise about
having two distinct levels of descriptions with distinct roles. In
particular, this allows for dealing both with an action as a
prescription for motor controls and as the expectation for what
state changes will be obtained as a result. It also allows one to relate
those two levels to each other.
| ... The deliberative level is the one that Pat alludes to, where actions
are characterized by discrete properties at a small number of timepoints:
possibly only the beginning and the end of the action, possibly a few
more, possibly a sequence of partial world states at integer timepoints
(as in basic Features and fluents).
The fact that someone with Erik's insight seems to be unable to think of 'high-level' as meaning anything other than instantaneous situations is a vivid illustration of the problem Ive been complaining about: almost all our thinking in this field is dominated by the archaic and awkward oversimplifications embodied in the situation calculus.
David Poole wrote:
| What if I didn't know whether there was something on |
| No no. This is all a description of an action. .....
| I'll agree with David if the last sentence is changed to go "...it is
only sensible to attempt to carry out the action when the preconditions
are believed to hold". .....
Therefore, Pat, I don't understand what you are objecting against in
| (And what does it have to do with the original need for nonmonotonic
Im puzzled that you need to ask this question. Isnt this textbook-level stuff?