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by a low classification level data manipulation operation, the high
security level transaction will be reexecuted starting from reading that
blocked data to present a one-copy serializable schedule [92].
The work presented in this chapter offers several major contribu-
tions to the field:
• Implementing a secure multiversion concurrency control
model by modifying the Rajwinder Singh model [93] by
dividing the write set of the transaction into two parts, which
decreases the blocking time of high classification level trans-
actions and improves the response time
• Implementing a prototype to measure the performance cost
for dividing write set of the transaction into two parts in the
secure multiversion concurrency control model
• Proofing the correctness of the secure multiversion concur-
rency control model by using the criteria of security, serial-
izability, fairness, selection of correct data version, and fast
version selection
7.2 Related Work
Kim and Sohn presented a multiversion secure concurrency control
model that satisfies the integrity and security rules [94]. This model
used the information of the conflict transaction set and the lock and
made the scheduler decide if a new version could be accessed to a
high classification level data manipulation operation. This model is
free from the problem of the starvation of high classification level data
manipulation operations by presenting the conflict transaction set, the
invisible area, and the t-lock. Also, this model can improve the avail-
ability of the relational multilevel database security system by adding
the concept of version management, which uses the t-locks and write
timestamps. Kim and Sohn present the following definitions:
• Definition 1: A read/write set of a transaction T i is defined as
R -set T i / W -set T i . It contains the data that will be read/written
by the transaction T i . When the transaction T i is entered to
the scheduler, the scheduler gets R -set T i and W -set T i .
• Definition 2: The period between the times of the high clas-
sification level transaction, T H , is blocked by another low
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