How to handle global transactions in heterogeneous database systems

One of the most important problems in the field of integrated heterogeneous database systems is transaction management. It is not sufficient to integrate only data models and query languages. In order to provide equivalent access to integrated heterogeneous databases as to homogeneous databases, a global transaction management is required. The authors discuss several aspects of transaction management for heterogeneous database systems. Even though different existing database systems are involved in the execution of most transactions, global serializability and recoverability is required. The authors propose a three-level transaction model. At the top- and middle-level, the semantics of operations are used in order to achieve a high degree of concurrency. For bottom-level transactions, their model allows the use of transaction managers of existing systems without changes. If no autonomous local transactions are allowed, the model provides global transactions with full serializability and recoverability