A Research On Transaction Schedule Algorithm Of Security Database

In order to solve the transaction processing in multilevel security database, the ACIS-correct of multilevel secure transaction are studied in this thesis. The multilevel secure concurrency control algorithm base on snapshots and multilevel transaction schedule algorithm based on 2PL and serialization graph are presented. The research of multilevel secure concurrency control algorithm base on snapshots requires two snapshots of the database at all but the system highest security level. High-level transactions access snapshots of low-level data instead of accessing low-level data directly. Snapshots can prevent starvation of high-level transactions without introducing covert channels. The basic concepts of snapshots are explained and the concurrency control algorithm based snapshots is given. At last the multilevel transactions execution histories resulting from the algorithm proved to be serializable. Security correctness criterion is incompatible with traditional two-phase locking (2PL) in multilevel transaction environment, so trade-offs must be made between them. The research of multilevel transaction schedule algorithm based on 2PL and serialization graph are presented. In this thesis 2PL schedule is restricted in a single level and "soft lock" is used to eliminate covert channels caused respectively by 2PL and "read down" operations. This thesis uses serialization graph (SG) to make sure that transaction sections serialization order remains the same at every security level and the total multilevel transaction is serializable. This thesis gives the implementation of the algorithm and proves that it is A CIS-correct. We design the architecture of secure database and discuss some issues relative to implementation.