Before studying and categorizing MAS, we must first consider their most obvious alternative: centralized, single-agent systems. Centralized systems have a single agent which makes all the decisions, while the others act as remote slaves. For the purposes of this survey, a ``single-agent system'' should be thought of as a complex, centralized system in a domain which also allows for a multiagent approach.
A single-agent system might still have multiple entities -- several actuators, or even several robots. However, if each entity sends its perceptions to and receives its actions from a single central process, then there is only a single agent: the central process. The central agent models all of the entities as a single ``self.'' This section compares the single-agent and multiagent approaches.