One approach to task decomposition in the Soccer Server is to assign fixed positions to agents. Such an approach leads to several problems: i) short-term inflexibility in that the players cannot adapt their positions to the ball's location on the field; ii) long-term inflexibility in that the team cannot adapt to opponent strategy; and iii) local inefficiency in that players often get tired running across the field back to their positions after chasing the ball. Our introduced formations allow for flexible teamwork and combat these problems.
The definition of a position includes home coordinates, a home range, and a maximum range, as illustrated in Figure 4(a). The position's home coordinates are the default location to which the agent should go. However, the agent has some flexibility, being able to set its actual home position anywhere within the home range. When moving outside of the max range, the agent is no longer considered to be in the position. The home and max ranges of different positions can overlap, even if they are part of the same formations.
A formation consists of a set of positions and a set of units. The formation and each of the units can also specify inter-position behavior specifications for the member positions. Figure 4(b) illustrates the positions in one particular formation, its units, and their captains. Here, the units contain defenders, midfielders, forwards, left players, center players, and right players.
Figure 4: (a) Different positions with home coordinates and home and max ranges. (b) Positions can belong to more than one unit.
Since the players are all autonomous, in addition to knowing its own position, each one has its own belief of the team's current formation along with the time at which that formation was adopted, and a map of teammates to positions. Ideally, the players have consistent beliefs as to the team's state, but this condition cannot be guaranteed between synchronization opportunities.
Our team structure allows for several significant features in our simulated soccer team. These features are: (i) the definition of and switching among multiple formations with units; (ii) flexible position adjustment and position switching; (iii) and pre-defined special purpose plays (set plays).