A classification of update methods for replicated databases

In this paper we present a classification of the methods for updating replicated databases. The main contribution of this paper is to present the various methods in the context of a structured taxonomy, which accommodates very heterogeneous methods. Classes of update methods are presented through their general properties, such as the invariants that hold for them. Methods are reviewed both in their normal and abnormal behaviour (e.g., after a network partition). We show that several methods presented in the literature, sometimes in independent papers with no cross-reference, are indeed very much related, for instance because they share the same basic technique. We also show in what sense they diverge from the basic technique. This classification can serve as a basis for choosing the method that is most suitable to a specific application. It can also be used as a guideline to researchers who aim at developing new mechanisms.