Transaction management in federated database management systems (FDBMS) is compared with multi-level transaction management. An FDBMS has global and local transaction management and can therefore be viewed as a multi-level system. In order to cope properly with local transactions, a dynamic conflict relation between global subtransactions is introduced. By exploiting the knowledge about the context of the conflicts between global subtransactions, the authors derive a weaker form of multi-level serializability that is equivalent to quasi-serializability. The approach is further extended to exploit the semantics of the high-level operations that correspond to global subtransactions, even in the presence of local transactions. As a consequence, aborts of global transactions must be implemented by compensating subtransactions, and complete serializability is required for the resulting executions. A locking protocol is proposed that allows the coexistence of global multi-level transactions and local transactions, and the required cooperation by the underlying DBMSs is discussed.
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