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As mentioned previously, using execution traces as a basis for future
coordinated plans allows the
actors to learn plans beyond the scope of the first-principles planner (or
a traditional
second-order planner based on it). Another example shows how lifter L2
learns to interleave two
goals. This is the most useful segment lifters learn in the current
version of the system. The
usefulness of this procedure lies in the fact that it involves little idle
time and is much
more widely applicable than procedures involving more boxes. In this
example, HTO and L1 will act
as in the first example, with the box in question now an extra-large box
XLBOX1 rather than MBOX3.
The following are L2's plans and actions, starting four steps before HTO
makes her first request to
L1.
- 1.
- L2 creates a typical plan to get XLBOX1 onto the truck: to lift,
carry and load the box
jointly with L1. L1 agrees to lift the box together and they do so. L1
then agrees to carry the
box to the street. However, XLBOX1 is too large to carry, even jointly,
and the action (and
hence rest of the plan) fails.
- 2.
- L2 creates a plan to get SBOX4 onto the truck. The plan consists of
putting down XLBOX1
with L1's help and then lifting, carrying and loading SBOX4 onto the truck
by herself. L2 is
delayed in asking for L1's assistance because HTO calls first with a request
to put XLBOX1 onto HANDTR2. L1 agrees to help HTO.
- 3.
- When L2 does ask L1 to help achieve HAND-EMPTY via putting XLBOX1
down together, L1 replies
that she would rather load the box together onto the hand-truck. L2's
planner adapts her current
plan by replacing the PUT-DOWN-TOGETHER with the appropriate
LOAD-TOGETHER. The actors then load
XLBOX1 onto the hand-truck.
L2 continues on with her plan and loads SBOX4 onto the truck. Meanwhile,
HTO has pushed the
hand-truck to the street and L1 has agreed to get XLBOX1 onto the truck.
- 4.
- L2 constructs a plan to get large box LBOX2 onto the truck and moves
back to ROOM1.
- 5.
- L2 is interrupted before attempting to lift LBOX2 by a request from
L1 to help unload XLBOX1
from the hand-truck. L2 constructs the plan of moving to the street and
then unloading XLBOX1.
The actors do so.
- 6.
- L1 asks L2 to load XLBOX1 onto the truck and they do.
The sequence of actions L2 undertakes corresponds to six different calls to
the planner.
Nonetheless, L2 can extract a single coordinated procedure from her
execution traces by the
machinery of procedural
memory (showing the original literals instead of new variables for clarity):
((LOAD-TOGETHER XLBOX1 HANDTR2)
(LOAD SBOX4 TRUCK1)
(LOAD-TOGETHER XLBOX1 TRUCK1))
Next: 5. Experimental Analysis
Up: 4. Memory of Coordinated Behavior
Previous: 4.6 Storing Execution Trace Segments in Memory
Last Update: March 10, 1999
by Andy Garland