Résumé
Controlling concurrent accesses to shared data manipulated simultaneously by several users, as well as recovering from rejects and failures, are essential components of any current data system, especially databases. We highlight the inherent limits of the main criterion of the field : commutativity of operations on abstract data types. These limits convince us to rely on simple techniques, especially in the forthcoming works. Next, we propose a concurrency control technique fitted to object-oriented databases since it uses the inheritance graph. This proposition generalizes the only one which, to our knowledge, has been implemented: the protocol of ORION. Combining theoretical limits of commutativity with the notion of methods, which encapsulate the behaviour of objects, leads us to a simple, yet sufficient, technique for determining commutativity of methods. This last proposal combines the advantages of the previous proposition with the ones obtained, indirectly, by the first normal form constraint in relational databases.