  In this paper we give a thorough presentation of a model proposed by Tononi
et al. for modeling \emph{integrated information}, i.e. how much information is
generated in a system transitioning from one state to the next one by the
causal interaction of its parts and \emph{above and beyond} the information
given by the sum of its parts. We also provides a more general formulation of
such a model, independent from the time chosen for the analysis and from the
uniformity of the probability distribution at the initial time instant.
Finally, we prove that integrated information is null for disconnected systems.
