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Date:         Tue, 1 Sep 1992 12:40:50 PDT
From:         Penni Sibun <sibun@PARC.XEROX.COM>
Subject:      Re: Misunderstandings & miscellany
X-To:         CSG-L%UIUCVMD.BITNET@pucc.princeton.edu
              26 Aug 1992 20:43:29 -0700
              <92Aug26.204617pdt.11985@alpha.xerox.com>

(ps 920901.1200)

   [From Bill Powers (920826.2000)]

   ----------------------------------------------------------------------
   Penni Sibun (previous posts) --

   >From all the comments by others, I suspect that I misunderstood your
   last post in most of the possible ways. My apologies. As Avery said,
   we are ALL arguing against somebody else's point of view without
   really understanding it. You keep your temper remarkably well, which
   should be a lesson to all of us.

well, thanks.  i'm not so sure about that though....


   [From Bill Powers (920827.0800)]

   ----------------------------------------------------------------------
   --
   Penni Sibun (920826) --

   I'm being cautious here to avoid more podiphagia.

   You say
   >the interactionist argument is in general deemphasizes individuals
   and >emphasises their interactions.

   Does this mean that interactionists believe that interactions can be
   EXPLAINED without reference to the properties of individuals, or that
   they can be DESCRIBED without such reference?

i don't think i mean either.  we fall into our language problems here
though.  maybe we can say that interactionists think that you can't
describe or explain the individual w/o also the interaction.

   Does the interactionist
   viewpoint differ from, say, that of conventional sociology, in which
   it is held that there are laws of social systems that exist apart
   from, and indeed unconnected to, laws of individual behavior?

yes, indeed.  a primary interactionist field, ethnomethodology, came
about explicitly in reaction to sociology.  rather than asking ``how
can we describe there here institutions,'' it asks, ``are there
institutions, and if so what, and if so how constituted.''

   ------------------------------------------------------------------
   I have a copy of a '92 paper for AAAI (whatever that is)

american association for artificial intelligence.

   by Agre and
   Horswill called "Cultural support for improvisation." In it he

``they''!!

the theory is certainly primarily agre's, but horswill is the one who
wrote toast.

   Before this section, the authors discuss the philosophy of their
   approach, which depends on using the properties of objects in the
   environment to replace a great deal of computation. Here's my
   interpretation of what they say; make allowances for the fact that I'm
   trying to swim through a sea of unfamiliar terminology. Gratuitous
   comments by me are in square brackets.

   Objects in the world are characterized by the roles they play in
   customary routine activities. [The playing of roles is attributed to
   the objects. A lot of the language that follows could be cleaned up by
   inserting "are perceived to be" or some such proviso at frequent
   intervals].

well, ``playing a role'' is a well-understood way of talking about
these things.  the advantage of talking about roles instead of
perceptions, is that you don't have to ask perceived by whom.

   A given object type is characterized by a state graph: nodes are
   states and arcs are labeled as operations that change the state from
   one node to another. [These are apparently thought of as properties of
   the objects, but operations are defined in terms of their outcomes,
   not in terms of the actions that bring them about. In HPCT terms, the
   operations could be re-phrased as the setting of goals specifying a
   new state which lower systems then bring about, thus moving the object
   state to the new node].

   An operation can be a label that applies to several arcs leaving a
   given node, thus being "nondeterministic." [This baffles me. Do they
   mean "stochastic?" Do they mean that under various circumstances, a
   given act can have different outcomes?

they defined it:  ``in the sense that it labels several arcs leaving
from the same state.''  the terminology is straight from computer
science theory:  a machine is deterministic if there is only one way
to get from one state to the next; it's nondeterministic otherwise.

the point is that there's more than one way to get from one state to
another.

   A world state is a set of instances and a mapping from each of these
   instances to a state in its type's graph. A history follows a set of
   instances through a series of changes. [This would seem to amount to a
   model of the environment's behavior]

no, a history is what happens between one point in time and another
point in time.

   An action type is a sequence of pairs made of an object type and an
   operation from that type's state graph.[ So an action type is a set
   sequence of operations that produces a set sequence of states.

it's not a set sequence of states if the operations are
nondeterministic.  it's a set of possible sequences.
   A goal for an object is satisfied if the world state contains some
   instance of the object type that is in the indicated state.(So one
   cannot assert that two instances of a given type must be in a given
   state). [I don't see the advantage of this rule. It says, apparently,
   that the goal of breaking a given egg is satisfied if the egg being
   operated on remains intact, but another egg breaks.

no, it says that the goal of breaking an egg is satisfied if an egg
(any old egg) is broken.  it doesn't have to be egg-47 or egg-13.

   So the only egg that can
   break is the one being operated on by the break operation and there's
   no need to keep track of which egg is broken.]

that's true.  why do you find this contradicts the above?

   Summing up, the authors give this description of the algorithm:

   While there are unsatisfied goals,

   Choose aribtrarily an unsatisfied goal.

   Let G be the specified goal state.

   Find an instance M of the specified material type.

   Determine its current state S.

   Let A be the entry for the S and G in M's action table.
   Choose tool instances to fill each of A's participant slots,
   preferring instances which are already in their normal state.

   If some chosen tool T is not in its normal state, then perform the
   action specified in T's action table for its current state. Otherwise
   perform A using M and the chosen tools.
   ----------------------------------------------------------------------
   -
   This last summary is ever so much simpler than all the verbiage that
   led up to it, because the attempt to present a general case has been
   reduced to a specific case.

in what way is it specific?

   One change I would suggest is the explicit addition of an error graph
   for each operation. The main weakeness of this algorithm as it stands
   is that every operation must produce a predictable state. By using an
   error graph this limitation could be removed.

yes, i agree.  it would at least be interesting.


it would certainly be interesting if you (or someone wanted to try to
incorporate your suggestion into toast.  it would be instructive for
everyone, i'm sure.  i think you can get the code from horswill,
though i would guess it's all in lisp.

cheers.

				--penni
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