  We propose an extension of Hybrid I/O Automata (HIOAs) to model agent systems
and their implicit communication through perturbation of the environment, like
localization of objects or radio signals diffusion and detection. The new
object, called World Automaton (WA), is built in such a way to preserve as much
as possible of the compositional properties of HIOAs and its underlying theory.
From the formal point of view we enrich classical HIOAs with a set of world
variables whose values are functions both of time and space. World variables
are treated similarly to local variables of HIOAs, except in parallel
composition, where the perturbations produced by world variables are summed. In
such way, we obtain a structure able to model both agents and environments,
thus inducing a hierarchy in the model and leading to the introduction of a new
operator. Indeed this operator, called inplacement, is needed to represent the
possibility of an object (WA) of living inside another object/environment (WA).
