critical design feature of the system itself ( L. Gasser, personal communication). User interaction with the technical system requires support for three separate flows of information: interactions between the user and the system interfaces; interactions with and understanding of the technical system being controlled; and interactions between the interfaces and the system. (Technically, the user's understanding of technical system behaviour is also limited by the technical system's accurate representation of the "real world" and how system dynamics are influenced by it. In many cases, this fourth flow of information is not an important element of most mature complex systems. However, when the system is being operated in unfamiliar conditions, of the behaviour of the system itself is unknown, the consequences of degraded information flow can be disastrous.)
From an engineering perspective, the property of connecting changes in one system component to changes in another system component is known as coupling. This concept allows us to develop improved methods of understanding the impact of degraded information flow and the dangers of removing feedback between the human and important system elements. (When coupling between components is zero, actions of one component have no influence on actions of another component.) The following figure illustrates the important sources of coupling in a human-system interface.
Informated systems, therefore, rely on the existence of reliable information flow between users and technical systems, and the design of transparent interfaces