Reactive agents constitute the last level of the architecture. Interactions between reactive agents are provided by signals, as stimuli-reactions. Signals do not bear semantics, and their meaning depends on the interpretative ability of the receiver. Some parameters define the agent's state, and are called state parameters. An agent is assumed to be stable when the values of his state parameters do not hit thresholds (that is, critical values). Thresholds and state parameters are given by the designer before the simulation begins.