Nunamaker [1991] and Rodden [1991] distinguish environmental facets of group work. These include the form of interaction (or time dimension) and the geographical dispersion of the group members (or spatial dimension):
Computer-mediated communication can be either synchronous or asynchronous in time. In case of synchronous communication group members interact directly, in real-time, with one another. Examples of synchronous interaction are face-to-face meetings and telephone conversations. Computer-mediated synchronous communication is particularly found in conferencing systems like automated meeting rooms or teleconferencing systems.
Opposite to real-time cooperation is asynchronous or non real-time cooperation. Communication cycles in asynchronous conversation can take a considerable amount of time to complete whereas in synchronous interaction these are typically short. Examples of asynchronous interaction include written documents, both personally addressed as well as impersonally addressed. Computer-mediated asynchronous communication appears in message systems such as electronic mail, which even support interaction over long geographical distances. Media for asynchronous communication generally impose less constraints on the group members than media for synchronous communication.
Group members can work together at one place (co-located) or geographically dispersed over many locations (remote). As Rodden [1991] rightfully points out, this division is concerned with the accessibility of users to each other rather than their absolute physical proximity. Examples of co-located interaction are group meetings. An automated meeting room is an example of a computer-mediated co-located communication facility. Means for communication between distributed group members are the telephone and written documents. Of course, letters may be send by electronic mail.
A different classification of CSCW systems is based on characteristics of the group task. Combining these with the criteria presented here, yields Rodden's famous classification space of CSCW systems:
Sjoerd Michels, Tilburg, The Netherlands