The important thing to note is that these non-functional differences such as pace and ease of interaction can make profound differences to the content of communication. In the mail example, the total system consists of the medium and the people who are communicating. In general systems have other active members than just the humans and we refer to both types of active member as agents . The final classification, objects refers to those components which are passive, but are not merely artifacts of the interface, for instance data- files. The distinctions introduced can be used purely descriptively or normatively in judging existing or putative systems.
Window managers are less interventionist leaving the application to shape the media.
However many systems involve computation and change even when not authoring. Depending on users' perception of the active and passive roles of system components they will make different inferences about their possible behaviour and integrity. Clarifying the distinction between the hypertext as media and computer agents that act on it, simplifies the situation and suggests possible improvements to the conceptual design. By analysing appropriate real world situation in terms of agents and media, we can make recommendations as to which parts of a computer system should be subject to adaptivity. In particular, in human dialogue, the medium does not change.