In a multilevel secure database management system based on the replicated architecture, there is a separate database management system to manage data at or below each security level, and lower-level data are replicated in all databases containing higher-level data. The issue of transaction processing in such a system is addressed. A synchronization protocol is given that guarantees one-copy serializability of concurrent transaction executions. It is secure since the information always flows in one direction-from databases at lower security classes to databases with higher security classes-and it can be implemented in such a way that the size of the trusted code (including the code required for concurrency and recovery) is small.
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