A Framework for Flexible Transaction Management in Multidatabase Systems

Global transaction management and the preservation of local autonomy present conflicts to the design of multidatabase transaction management systems. A flexible transaction model for the specification of global transactions has been proposed to enhance global transaction management while preserving local autonomy. This paper presents a theory of flexible transaction management that is applicable in those situations where local database systems maintain only serializability and recoverability. A fundamental characterization of the model and of the properties of flexible transactions is first offered. The meaning of relaxed atomicity and isolation of flexible transactions is precisely defined. We then investigate the principles of flexible transaction management that are necessary for ensuring these properties. A class of flexible transactions, which can be executed in the presence of failures, is constructed, and a new correctness criterion is proposed. The results demonstrate that the flexible transaction model enhances substantially the scope of global transaction management beyond that offered by the traditional global transaction model.