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4.2 Cleaning the execution trace

As discussed in Section 3.3 actors abandon plans and switch top-level goals for a variety of reasons at runtime. This means the execution trace may contain actions that should not be part of learned cooperative procedures. The goal of the cleaning process is for actors to remove such actions, while preserving consequential ones.



Remove any event E with action A in trace if any of the following hold:
Figure 5: Algorithm to clean traces.

An actor can remove an action from the execution trace for one of several reasons (see Figure 5). The justifications for all but the last two pruning criteria are fairly self-evident. The last two rules are designed to weed-out operators that seemed to be useful at the time, but eventually were not. The penultimate criterion removes actions which were either undone by a later action or which recreated the same setting. For example, (LOAD BOX1 BOX2) is undone by (UNLOAD BOX1 BOX2) and vice versa. Further, (UNLOAD BOX1 BOX2) can recreate the same setting as (LIFT BOX1) so the sequence

  (LIFT BOX1) (LOAD BOX1 BOX2) (UNLOAD BOX1 BOX2)

is reduced to merely the (UNLOAD BOX1 BOX2) action by this criteria.

For an example of an action removed by the last criterion, suppose a hand-truck operator (HTO) gets a lifter (L1) to load a box onto a hand-truck, which HTO then pushes to the street and stands up. Suppose further that no lifter agreed to unload the box when it was at the street and HTO eventually pushed the hand-truck containing the box back to the box's original location. At this point, L1 unloads it from the hand-truck, carries it (back) to the street and loads it onto the truck. In this case, HTO's request did not help to achieve the goal and should be removed from the summary.


Next: 4.3 Segmenting the Execution Trace Up: 4. Memory of Coordinated Behavior Previous: 4.1 A simple learned coordinated procedure
Last Update: March 10, 1999 by Andy Garland