A group has a shared state and the members of the group operate on the shared state by accessing and modifying the shared objects in the shared state. Corona requires that a process has to be a member of a group in order to operate on the shared state of the group. The group members communicate with each other by exchanging messages among themselves. Corona supports both unicast and group multicast communication. Total ordering delivery semantics can be ensured by sequencing the messages in the server.
Corona provides interfaces for c reating, deleting, joining, leaving a group, etc.
It also provides support for an important social aspect of collaboration, awareness - users collaborating over shared state want to be aware of each other and their activities. The system makes this information available to client applications, via queries to the server or notifications of membership changes. The shared state of a group in DistView is maintained by the server, as opposed to other multicast systems, where the state of the group is maintained by the clients. In this sense, the server is stateful . A group may be characterized as either persistent or transient.