So far, we have seen two forms of locking: coarse-grained floor control in RTCAL and fine-grained concurrency control in CES. We now see an example of a commercial multiuser application, Aspects [], which provides multiple models of concurrency control and a special user-interface for explicitly getting and releasing locks.
In Aspects, a conference is created by a special user called a moderator, who has special access rights.
It supports three modes of concurrency control or ``mediation'' and the exact one used is determined dynamically by the moderator. In the ``free for all'' mediation mode, locking is at the paragraph level. A user editing a paragraph sees a black bar on the side of it and other users see a grey bar. In the ``medium mediation'' mode, access to the complete document is serialized and users use a pen passing mechanism to pass control. A user can be writing, waiting for a pen, or just observing. Pen icons are used to pass control. A user can click on his closed pen icon to request the pen. The user's icon starts blinking and turns into a raised hand and the writer's open icon also starts blinking. The writer can click on the ``pen in hand'' icon to pass control to the first person waiting. Clicking on a black arrow shows the pen status of the different participants. In the ``full mediation'' mode, access to the document is again serialized but this time the moderator determines who gets the pen next after it has been relinquished.
Like Cognoter, Aspects provides support for gesturing by
associating each user with a unique telepointer whose position is viewed by all users.
In Aspects, upto 16 people can be in a conference simultaneously.
When the conference is closed, everyone is sent a message informing them about the termination