In multi-level secure database management system (MLS/DBMS), every transaction and data has associated with a unique security. Concurrent transactions on MLS/DBMS potentially have conflicts while accessing the shared data. The conflicts result in some of the conflicting transactions to be delayed. If the delayed transactions have been cleared at low security level, an information may flow downward with the violation of security policy. This kind of communication channel is called covert channel.
Several transaction scheduling schemes for solving the covert channel problem had been presented. Although they had solved the covert channel problem, unfortunately, they had left alone other kinds of security problems, such as the availability and the integrity problems. Since computer security consists of maintaining the confidentiality, the availability, and the integrity, an attempt to acquire every characteristic is necessary.
Tightly secure transaction scheduler, presented in this paper, schedules concurrent transactions without loss of the characteristics of security. For the confidentiality and the availability, the philosophy of the scheduler is based on the concealment of uncommitted data. Besides, for the integrity, a trustworthiness together with a recentness of a data are considered for discriminating the appropriateness of the data.