Next: ENVIRONMENTSPOLICIES, AND REDUCIBILITY
Up: Lifeworld Analysis
Simon, in Sciences of the Artificial
, argued that complex systems
had to be ``nearly decomposable.'' His model for this was the rooms
in a building, whose walls tend to minimize the effects that activity
in one room has upon activity in another. Sussman
, in his analysis of block-stacking tasks,
classified several types of ``subgoal interactions'' that result from
attempts to break tasks down into subtasks; one hopes that these tasks
will be decomposable, but bugs arise when they are not decomposable
enough. One assumes that a task is decomposable unless
one has reason to believe otherwise. Sussman's research, and the rich
tradition of planning research that it helped inaugurate, concerned
the difficult problem of constructing plans in the presence of subgoal
interactions. Our goal, complementary to theirs, is to analyze the
many ways in which tasks really are decomposable, and to derive the
broadest range of conditions under which moment-to-moment activity can
proceed without extensive analysis of potential interactions.
A non-pathological lifeworld will be structured in ways that limit or
prevent interactions among subtasks. Some of these structures might be
taxonomized as follows:
- Activity partition. Most lifeworlds separate activities under
discrete headings: sewing is a distinct activity from bathing, gathering
food is a separate activity from giving birth, and so on. These distinctions
provide the basis for reckoning ``different activities'' for the purposes
of most of the rest of the partitions. The boundaries among the various
activities are often marked through some type of ritual.
- Spatial partition. Different things are often done in different
places. Tasks may be confined to the places where their associated tools
or materials are stored, or where suitable conditions or lighting or safety
obtain. These places may even be close together, as when different recipes
are prepared in different sections of countertop space or different kinds of
food are kept in different parts of one's plate, with boundary regions perhaps
employed to assemble forkfuls of neighboring foods. In general, activities
are arranged in space, and decisions made in one place tend to have minimal
interaction with decisions made in other places. Of course spatial distance
brings no absolute guarantees about functional independence (using up all
the resources at one location will prevent them from being carted to another
location for another use later on), so these are just general tendencies.
- Material partition. Different activities often involve different
materials, so that decisions that affect the materials in one activity do not
interact with decisions that affect the materials of the other activity.
- Temporal partition. Different activities often take place at
different times, thus limiting the channels through which they might constrain
one another. These times might be standardized points during the cycle
of the day or week, or their ordering might be constrained by some kind of
precondition that the first activity produces and successive ones depend upon.
- Role partition. Simon pointed out that division of labor eases
cognitive burdens. It does this in part by supplying individuals with
separate spheres in which to conduct their respective activities.
- Background maintenance. Many activities have background
conditions that are maintained without reference to specific goals.
For example, one maintains stocks of supplies in the pantry, puts things
back where they belong, and so forth. Hammond, Converse, and Grass
 call some of these ``stabilization.''
(See Section 5.) What these practices stabilize are the relationships
between an agent and the materials used in its customary activities.
They tend to ensure, for example, that one will encounter one's hammer
or the currently opened box of corn flakes in definite sorts of
recurring situations. They thus reduce the complexity of life, and
the variety of different hassles that arise, by encouraging the rise
of routine patterns and cycles of activity rather than a constant
stream of unique puzzles.
- Attributes of tools. Numerous properties of tools limit the
interactions among separate decisions. Virtually all tools are resettable,
meaning that regardless of what one has been doing with them, they can be
restored to some normal state within which their full range of functionalities
is accessible. (This of course assumes that one has only been using the tools
in the customary ways and has not been breaking them.) Thus the properties of
the tool do not place any ordering constraints on the activities that use it.
Likewise, most tools are not committed to tasks over long periods. Once you
have turned a screw with a screwdriver, for example, the screwdriver does not
stay ``stuck'' to that screw for any long period. Thus it is not necessary
to schedule the use of a screwdriver unless several people wish to use it at
once. Exceptions to this general rule include bowls (whose ingredients must
often sit waiting for future actions or conditions, and which cannot
contain anything else in the meantime), stove burners (which sometimes must
remain committed to heating particular dishes until they have reached certain
states and not before), and clamps (which must remain fastened until the glue
has dried or the sawing operations have been completed).
- Supplies of tools. These latter tools raise the spectre of
generalized scheduling problems and the potential for deadlock among multiple
activities, and such problems do in fact sometimes arise when cooking for more
people than the number to which a given kitchen is adapted. Most of the time,
though, one solves such problems not through scheduling but simply through
having enough of the tools that must remain committed to particular purposes
over a period of time. Lansky and Fogelsong  modeled
the effects on search spaces of limited interactions between different cooks
using overlapping sets of tools.
- Warning signs. When things go wrong, unpleasant subgoal
interactions can ensue. To avoid such difficulties, an individual, community,
or species keeps track of warning signs and cultivates the capacity to notice
them; these warning signs include supplies running low and funny smells.
This is often done on a primitive associative level, as when rats stay away
from smells that were associated with stuff that made them sick or people
develop phobias about things that were present when they suffered traumas.
Communities often arrange for certain warning signs to become obtrusive,
as when kettles whistle or natural gas is mixed with another gas that has
a distinctive smell.
- Simple impossibility. Sometimes things are just
impossible, and obviously so, so that it is not necessary to invest
great effort in deciding not to do them.
- Monotonicity. Many actions or changes of state are
irreversible. Irreversible changes cause decisions to interact when
certain things must be done before the change takes place. But it
also provides a structure for the decision process: the lifeworld
needs to make it evident what must be done before a given
irreversible change occurs.
- Flow paths. Often a lifeworld will be arranged so that
particular materials (parts on an assembly line, paperwork in an
organization, food on its way from refrigerator to stove to table)
follow definite paths. These paths then provide a great deal of structure
for decision-making. By inspecting various points along a path, for
example, one can see what needs to be done next. Or by determining
where an object is, one can determine what must be done to it and
where it must be taken afterward. Some of these paths are consciously
mapped out and others are emergent properties of a set of customs.
- Cycles. Likewise, many lifeworlds involve stable
cycles of activities, perhaps with some of the cycles nested inside
of others. The resulting rhythms are often expressed in recurring
combinations of materials, decisions, spatial arrangements, warning
signs, and so on.
- Externalized state. To computer people, ``state'' (used
as a mass noun) means discernible differences in things that can be
modified voluntarily, and that can be
interpreted as functionally significant in some way. Early AI did
not treat internal state (memory) and external state (functionally
significant mutable states of the world) as importantly different,
and it is often analytically convenient to treat them in a uniform
fashion. It is often advantageous to record state in the world,
whether in the relative locations of things and the persistent states
(in the count noun sense) that they are left in .
For example, one
need not remember whether the eggs have been broken if that fact
is readily perceptible, if one's attention will be drawn to it on a
suitable occasion, and if one understands its significance for the
task. Likewise, one can save a great deal of memory by retrieving
all of the ingredients for an evening's recipes from the cupboards and
placing them in a customary place on the shelf.
Lifeworlds, then, have a great deal of structure that permits decisions to
be made independently of one another. The point is not that real lifeworlds
permit anyone to live in a 100% ``reactive'' mode, without performing any
significant computation, or even that this would be desirable. The point,
rather, is that the nontrivial cognition that people do perform takes place
against a very considerable background of familiar and generally reliable
The factorability of lifeworlds helps particularly in understanding
the activities of an agent with a body. A great deal of focusing is
inherent in embodiment. If you can only look in one place at a time,
or handle only one tool at a time, your activities will necessarily
be serial. Your attention will have a certain degree of hysteresis:
having gotten to work on one countertop or using one particular tool,
for example, the most natural step is to carry on with that same task.
It is crucial, therefore, that different tasks be relatively separate
in their consequences, that the lifeworld provide clues when a
change of task is necessary, and that other functionally significant
conditions can generally be detected using general-purpose forms of
vigilance such as occasionally looking around. Of course, certain
kinds of activities are more complex than this, and they require
special-purpose strategies that go beyond simple heuristic policies
such as ``find something that needs doing and do it.'' The point is
that these more complex activities with many interacting components
are rare, that they are generally conducted in specially designed
or adapted lifeworlds, and that most lifeworlds are structured to
minimize the difficulty of tasks rather than to increase it.
These various phenomena together formed the motivation for the concept of
indexical-functional or deictic representation
[4, 3]. Embodied agents are focused
on one activity and one set of objects at a time; many of these objects are
specifically adapted for that activity; their relevant states are generally
readily perceptible; objects which are not perceptibly different are generally
interchangeable; and stabilization practices help ensure that these objects
are encountered in standardized ways. It thus makes sense, for most purposes,
to represent objects in generic ways through one's relationships to them. The
flashlight I keep in the car is the-flashlight-I-keep-in-the-car and not
FLASHLIGHT-13. I maintain a stable relationship to this flashlight by keeping
it in a standard place, putting it back there when I am done with it, using
it only for its intended purposes, keeping its batteries fresh, and so on.
Its presence in the environment ensures that I have ready access to light when
my car breaks down at night, and therefore that I need not separately plan
for that contingency each time I drive. The conventional structures of my
own activity maintain the flashlight's presence as a ``loop invariant.'' Both
the presence of the flashlight and the activities that ensure it are
structures of my lifeworld.
Next: ENVIRONMENTSPOLICIES, AND REDUCIBILITY
Up: Lifeworld Analysis
Wed Apr 2 15:17:20 CST 1997