Michèle Cart

Concurrent operations in a distributed and mobile collaborative environment

In a distributed groupware system, objects shared by users are subject to concurrency and real time constraints. In order to satisfy these, various concurrency control algorithms have been proposed that exploit the semantic properties of operations (C.A. Ellis and S.J. Gibbs, 1989; A. Karsenty and M. Beaudouin-Lafon, 1993; C. Sun et al., 1996). By ordering concurrent operations, they generally guarantee consistency of the different copies of each object. However, in some situations they can result in inconsistent copies, a non respect of users intentions, and in the need to undo and redo some operations. The principle objective of the paper is to present an algorithm that overcomes these drawbacks in distributed and mobile collaborative environments. The algorithm is based on the notion of user intention, and also on the construction of equivalent histories by exploiting and combining some general semantic properties such as forward/backward transposition.

Serialization of concurrent operations in a distributed collaborative environment

In a distributed groupware system, objects shared by users are subject to concurrency and real-time constraints. In order to satisfy these, various concurrency control algorithms 141 [ 1 l] have been proposed that exploit the semantic properties of operations. By ordering concurrent operations, they guarantee consistency of the different copies of each object. The drawback of these algorithms is that in some situations they can result in inconsistent copies, a non-respect of user’s intentions, and in the need to undo and redo certain operations. The principle objective of the this paper is to present an algorithm that overcomes these problems. The algorithm is based on the notion of user’s intention, and also on the construction of equivalent histories by exploiting and combining some general semantic properties such as forward/backward transposition. Keywbrds: groupware systems, concurrency control, distributed systems, multi-user editors, operation transposition.

Integrating concurrency control into an object-oriented database system

In this paper, we describe the problems involved in integrating concurrency control into object-oriented database systems. The object-oriented approach places specific constraints on concurrency between transactions, which we discuss. We then propose an adaptation of the locking technique to satisfy them, without unnecessarily restricting concurrency. Finally, we analyse in detail the impacts of both the transaction model and the locking granularity imposed by the underlying system. The solutions proposed are illustrated with the O2 system developed by the Altair GIP.

Optimistic multi-level concurrency control for nested typed objects

The authors propose an optimistic multilevel method that also exploits commutativity of typed operations in order to enhance concurrency. One of the main advantages of this method is that it makes it possible to take commutativity depending upon return values into account. A bank-transaction example illustrating the proposed approach is presented.<<ETX>>