Collaboration can be classified according to whether the participants are interacting at a) the same or different ``times'' and b) the same or different ``place''. [ Ellis CACM ] The time and space dimensions together define four classes of collaborations: same time-same place, same time-different place, different time-same place, and different time-different place.
What does ``same place'' and ``same time'' collaboration mean exactly? Defining ``same place'' collaboration is not difficult - it is collaboration among a set of users that is enabled only when they go to some physical room.
Defining ``same time'' collaboration is more difficult. Here are three possible definitions:
Same time collaboration is WYSIWIS collaboration, that is, all users see an identical image and updates to it are sent immediately to all users. This is the strictest definition but disallows near-WYSIWIS collaborations such as those supported by Grove (it allows users to scroll independently), which one might consider as same time collaborations.
We do not require users to see the same image but assume only that they share some underlying state with possibly different visual manifestations. We do require that changes made by a user to this state are sent instantly to other users, that is, the application does not buffer changes before sending them to others. This is less strict than the previous one but maybe still too strict since one might want to allow some buffering to support ``think time''. Collaborations supported by Ensemble (which buffers changes until the item is unlocked) would not be considered as same time collaborations by this definition, yet Ensemble is used for ``meetings''.
Another definition may be that in same time collaboration, information is sent implicitly as a side effect of some other action, whereas in different time collaboration, explicit send and receive commands have to be executed. By this definition, an editor that implicitly sends hourly updates supports same time collaboration, which we may not agree with.
Same time collaboration occurs between users if each of them has explicitly executed a join command to join the conference. This definition excludes Ensemble, which allows users to implicitly join a conference by concurrently editing the same file.
We can say that two users are interacting at the same time if a user's communication to the other is immediately processed by the other as soon as it is received by the latter. In other words, the two users are in a ``meeting'' where each user is paying immediate attention to the other's communication. (A user is free to take time in processing a message and do other tasks while the other user is thinking or messages are in transit - an in real meetings.) In technical terms, same time collaboration implies that users receive responses to their messages within some threshold ``attention-keeping'' time, which may depend on how patient the users are. To make our discussion simple, let us assume that there is a some universal number that applies to all groups.
Assuming we choose one of these definitions of same time collaboration, we can classify collaborative applications according to the class of collaboration they can support. A collaborative application may support more than one of these classes. In particular, an application used for different place collaboration can also be used for same place collaboration, though it may have redundant features such as displays of participants. Moreover, an application that supports same time collaboration also supports different time collaboration if we use the last definition of same time,
more than the ``attention keeping'' time before they respond to each other. Furthermore, an application that supports same place collaboration may also support different place collaboration if we assume they can talk to each other over the telephone.
To make our discussion simple, we will say an application supports same place/different time collaboration if it can only support same place/different time collaboration.
Moreover, we will say that an application supports different time collaboration if it always imposes a delay of more than attention keeping time in delivering messages. Furthermore, we will assume that users cannot use any communication media except those supported by face to face interaction or explicitly by the application. In particular, they cannot use an audio or video telephone. This is consistent with what others assume when they use this taxonomy. Finally, we will say an application supports different place collaboration if it has some feature such as discussion windows and displays of lists of participants that would be ``redundant'' in a same-place collaboration.
So let us classify our tools according to this taxonomy.
Same time-same place: rIBIS, Cognoter, Tivoli.
Same time-different place: RTCAL, CES, GROVE, Groupsketch, Groupdraw, Ensemble (the prev three are in this class because of gesturing support), GroupDesign, Mercury, MUD, Video Walls, Shared Awareness Space (is it fair to call it same time?), and 3-D Aura.
Different time-same place: Physical bulletin board.
Different time-different place: Information Lens, Coordinator, ActionWorkflow, Mercury, Chronicle, and MUDs with mail.