DUPLEX is a distributed collaborative editor for users connected through a large-scale environment such as the Internet. Large-scale implies heterogeneity, unpredictable communication delays and failures, and inefficient implementations of techniques traditionally used for collaborative editing in local area networks. To cope with these unfavorable conditions, DUPLEX proposes a model based on splitting the document into independent parts, maintained individually and replicated by a kernel. Users act on document parts and interact with co-authors using a local environment providing a safe store and recovery mechanisms against failures or divergence with co-authors. Communication is reduced to a minimum, allowing disconnected operation. Atomicity, concurrency, and replica control are confined to a manageable small context.

The authors present the definition of and solution to the uniform reliable multicast problem in the virtually synchronous environment defined by the Isis system. A uniform reliable multicast of a message m has the property that if m has been received by any destination process (faulty or not), then m is received by all processes that reach a decision. Uniform reliable multicast provides a solution to the distributed commit problem. Two multicast primitives are defined in the virtually synchronous model: reliable multicast (called view-atomic) and uniform reliable multicast (called uniform view-atomic). The view-atomic multicast is used to implement the uniform view-atomic primitive. As view-atomicity is based on the concept of process group membership, a connection is established between the process group membership and the distributed commit problems.>

A pessimistic consistency-control algorithm is presented. The principle of the algorithm is to order transactions dynamically in the global serialization graph of the system. This order is built by associating numbers with transactions in such a way that these numbers decrease along any path in the graph. Transaction numbers correspond to an arbitrary ordering of replicated objects. The model of the distributed system and the transaction manager are described. Replicated objects and the basic access strategy used to illustrate the method are introduced. Both the access algorithm, with a proof of its correctness, and the recovery algorithm are described. The generalization of the method to other pessimistic algorithms and several related issues are discussed.>