As developed in reactive planning research, Situation Spaces structure the states of the world into situations and links between situations. The behavior of the agent is organized around its current situation which determines both the (sub)goal(s) it should try to achieve (or maintain) and how to monitor the world. In turn, monitoring determines whether traversal to a new situation has occurred. Traversals could be caused by successful achievement of a (sub)goal, as well as fortuitous or bad turn of events. Therefore, a traversal could be advantageous or dis-advantageous in terms of achieving the overall goal. Traversals through the situation space represent alternative abstract partial decomposition plans which can incorporate both purely goal-directed behavior as well as goal-directed responses to unforeseen events.
To make these ideas more concrete, consider the situation space depicted in Figure 3 for the simplified example problem presented earlier. Recall the problem was to travel in a wedge formation to a blocking position, responding to encounters with the opposing force en route.
The current situation at the start of the exercise is assumed to be ``Traveling'' (Wedge Formation). As noted above, the current situation determines the goals to achieve. When a platoon is in this Traveling situation, their goals include traveling along some route towards the blocking position, and the maintenance goals of maintaining a wedge formation and scanning for the enemy. As they pursue these goals, various kinds of expected or un-expected transitions can occur which must be monitored for while in this situation. For instance, the students must monitor for reaching their objective, noted as the transition to the Goal situation. Also, they must monitor for contact with other forces. This could cause a transition to an ``Action on Contact''. If that transition occurs, the goals in this new situation would include assessing the threat, targeting opposing forces and insuring one is not a good target. (In actuality, actions on contact encompass different kinds of responses and one might expand this situation into several situations in order to explicitly capture these differences.) Again as noted by the transition arcs, when in the Action on Contact situation, transitions to ``Disabled'' or back to ``Traveling'' must be monitored.
Even from this simple example, several characteristics about situation spaces can be noted. There are multiple such paths through the space, in fact, an infinite number since looping is possible (between traveling and action on contact in this example). This compactly expresses the dynamic characteristics in these training environments whereby students can undergo repeated and unexpected encounters. The situation space models the necessary reactivity within an overall goal-directed declarative plan. At the same time, the situation space does not separately represent each possible plan - to do so would be implausible. Rather, the situation space models sets of possible plans at a high level, with each situation modeling many possible problem solving histories. Finally, the situation space is noncommittal concerning how the plan generation occurs within a situation or even what planning architecture should be used. Rather, it is a framework in which goal-directed behavior can be planned for and realized in a dynamic world.
Of course, our interest in situation spaces does not follow from an intent to use them for single agent planning. Rather, we saw situation spaces as a good declarative model around which to organize a pedagogical agent's analysis of team behavior in a dynamic world. As a consequence, we needed to transform them from an aid for planning to an aid for analysis of team behavior.
