A locking protocol for multilevel secure databases using two committed versions

This paper presents a locking protocol for secure databases which produces one-copy serializable and strict schedules. These schedules satisfy the multilevel security property-thus, the protocol is secure. The proposed protocol requires only two committed versions of the database; it executes read downs on the earlier committed version, while transactions accessing objects at their own level execute on the later committed version and are synchronized using strict 2PL. We discuss how the proposed protocol supports the execution of long-running transactions. The paper presents many useful details of snapshot maintenance for locking protocols in secure databases