3.5.1 Examples of coordinating joint activity

The following two examples show trace snippets involving cooperation in unloading a box from a hand-truck and loading it onto the truck. The examples are actual output of the system (with unrelated actions trimmed), but they are illustrative, not prototypical; empirically, actors agree to cooperate less than half of the time when they have different goals.

Figure 3 shows two traces generated by actors coordinating via first-principles. In the first case, L2 happens to have the same goals as HTO1 before conversing; in the second case, she does not. In both cases, HTO1 will add a WAIT operator to her plan as a result of the conversation with L2. When L2 and HTO1 had the same goals, their behavior is slightly more efficient because L2 moves to the street before HTO1 makes her request. However, this kind of timing is exceptional. HTO1's request is superfluous, but there is no way for the hand-truck operator to know this beforehand. The more typical case, when the actors have different goals, is shown in the lower half of the figure. As mentioned above, the biggest hurdle to be faced in this situation is getting agreement.

Same Goals

Round 15: <STAND-HANDTR HANDTR3 PR17-STREET1> done by HTO1
Round 15: <MOVE PR17-STREET1> done by L2
Round 16: HTO1 places a call to L2:
  "L2, would you help me achieve (ON PR17-MBOX7 TRUCK3)?"
  "HTO1, I'm already working on it!"
Round 17: <UNLOAD PR17-MBOX7 HANDTR3> done by L2
Round 18: <LOAD PR17-MBOX7 TRUCK3> done by L2

Different Goals

Round  7: <STAND-HANDTR HANDTR3 PR24-STREET1> done by HTO1
Round  8: HTO1 places a call to L2:
  "L2, would you help me achieve (ON PR24-MBOX8 TRUCK3)?"
  "HTO1, I'll help, but you'll have to wait a bit."
Round  9: <MOVE PR24-STREET1> done by L2
Round 10: <UNLOAD PR24-MBOX8 HANDTR3> done by L2
Round 11: <LOAD PR24-MBOX8 TRUCK3> done by L2

Figure 3: Coordination based on first-principles: L2 unloads the hand-truck for HTO1.

In Figure 4, the actors are working from plans which are derived from past joint activity and the lifter's plan contains a WAIT-FOR operator. Although the two actors are working from the same past interactions, L1 becomes frustrated waiting for HTO1 to make her expected explicit request. As it turns out, L1's inquiry came in the same round that HTO1 would have made the request, so the conversation proceeds smoothly. Note that, from an efficiency stand-point, this is no better than either of the first-principles solutions. However, in this case, the outcome is more robust: it does not depend on serendipitous timing or agreeable actors.

Round 10: <STAND-HANDTR HANDTR3 PR24-STREET1> done by HTO1
Round 11: L1 became frustrated since WAIT-FOR not satisfied
Round 11: L1 places a call to HTO1:
  "HTO1, I was expecting a call about (ON PR24-MBOX7 TRUCK3)."
  "L1, would you help me achieve (ON PR24-MBOX7 TRUCK3)?"
  "HTO1, I'll help, but you'll have to wait a bit."
Round 12: <MOVE PR24-STREET1> done by L1
Round 13: <UNLOAD PR24-MBOX7 HANDTR3> done by L1
Round 14: <LOAD PR24-MBOX7 TRUCK3> done by L1

Figure 4: Coordination based on explicit expectations: L1 unloads the hand-truck for HTO1.