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We achieve collaboration between agents through the introduction of formations. A formation decomposes the task space defining a set of roles. Formations include as many roles as there are agents in the team, so that each role is filled by one agent. In addition, formations can specify sub-formations, or units, that do not involve the whole team. A unit consists of a subset of roles from the formation, a captain, and intra-unit interactions among the roles.

For a team of n agents tex2html_wrap_inline1298 , any formation is of the form


where R is a set of roles tex2html_wrap_inline1302 such that tex2html_wrap_inline1304 . Note that there are the same number of roles as there are agents. However, it is possible to define redundant roles such that the behavior specification of tex2html_wrap_inline1306 is equivalent to that of tex2html_wrap_inline1308 ( tex2html_wrap_inline1310 ). Each unit tex2html_wrap_inline1312 is a subset of R: tex2html_wrap_inline1316 such that tex2html_wrap_inline1318 , tex2html_wrap_inline1320 and tex2html_wrap_inline1322 is the captain, or unit leader. The map tex2html_wrap_inline1324 is not fixed: roles can be filled by different homogeneous agents. A single role may be a part of any number of units and formations.

Units are used to deal with local problem solving issues. Rather than involving the entire team in a sub-problem, the roles that address it are organized into a unit. Captains are unit-members with special privileges in terms of directing the other unit members.

Roles and formations are introduced independently from the agents that are to fill them. The locker-room agreement specifies an initial formation; an initial map from agents to roles; and run-time triggers for dynamic changing of formations. At any given time, each agent has an opinion as to what formation the team is currently using. Agents keep mappings tex2html_wrap_inline1326 from teammates to roles in the current formation. All this team structuring information is stored in the agent's internal state. It can be altered via the agent's internal behaviors.

Since agents are autonomous and operating in a PTS domain, during the periods of limited communication there is no guarantee that they will all think that the team is using the same formation, nor that they have accurate maps tex2html_wrap_inline1328 . In fact, the only guarantee is that each agent knows its own current role. Thus, in our implementation of the teamwork structure, we create robust behaviors for team agents which do not depend upon having correct, up-to-date knowledge of teammates' internal states: they degrade gracefully. When limited communication is available, efficient low-bandwidth communication protocols can allow agents to inform each other of their roles periodically. Figure 3 illustrates a team of agents smoothly switching roles and formations over time.

Figure 3: A team of agents smoothly switching roles and formations over time. Different roles are represented as differently shaded circles. Formations are possibly overlapping collections of roles. Units within the formations are indicated within a dotted enclosure. The definitions of all roles, formations, and units are known to all agents. An agent's current role is indicated by the shaded circle in its head and its current formation is indicated by an arrow to the formation. The agents first switch roles while staying in the same formation; then they switch to an entirely new formation.

next up previous
Next: Set-Plays Up: Teamwork Structure Previous: Roles

Peter Stone
Thu Dec 17 15:26:44 EST 1998