Concurrency control frameworks for interactive sharing of data spaces in real-time distributed collaborations

The multimedia information exchanges in distributed collaborative applications may be modeled, from communication system perspective, as the flow of media messages between user entities, to provide access to shared window objects on workstations. An example of shared window is a design document interactively reviewed by a team of engineers over a discussion session. A key requirement is that all users should see the same local copy of a shared window object at any given point in time (WYSIWIS), even though these users may reside in different workstations interconnected over a network. In this paper, we study the temporal ordering of real-time persistent messages as the basis for achieving WYSIWIS. The approach requires specifying the synchronization constraints on accessing shared window objects in the form of state-transition relations and timeliness needs when processing messages for object state updates. Non-conflicting actions can be processed in any sequence by user entities, thereby increasing overall system-level performance and user-level efficacy. The paper describes the salient features of our concurrency control model, and then identifies the basic protocol elements to realize the model. Applications are also described to demonstrate the viability of our approach.