Database security theory and technology not only is an important research field of database theory, but also is an important research field of information security. In this paper, we improve BLP model by using master-slaver structure table. The extended BLP model not only has more system confidentiality but also has more availability and data integrity, comparing with the basic BLP Model. Security constraints are consistent by modifying security constraint definition, and an effective classification assignment algorithm is given in this paper. We analyze the problem of inference channel and give solution to solve the problem during database analysis and design period. By analyzing the problems resulting from extending single-level transactions to multilevel transactions, we also give a multilevel secure transaction schedule algorithm based multiversion snapshot graph. We develop an MLS/DBMS prototype system based above theories, and experimental results show these theories are correct. |