支持属性粒度数据库加密的查询重写算法

DAS（databaseasaservice）模型数据库中采用加密方案的关键问题之一是针对密文关系的查询处理．DAS模型特有的体系结构和信任模型决定了加密解密操作只能在客户端进行，目前的方案普遍在元组粒度加密的基础上进行查询重写，不可避免地造成了加密效率的损失．为此，提出一种支持属性粒度加密方案的查询重写算法，利用关系代数公式对查询语句进行等价变换，将涉及加密属性的条件谓词与其他条件谓词分离，重构查询语句，支持任意层次的相关子查询．实验显示，算法能够降低客户端与服务器间的网络传输数据量，从而有效地缩短加密DAS模型数据库的查询执行时间．

Holographic dual of linear dilaton black hole in Einstein-Maxwell-dilaton-axion gravity

Motivated by the recently proposed Kerr/CFT correspondence, we investigate the holographic dual of the extremal and non-extremal rotating linear dilaton black hole in Einstein-Maxwell-Dilaton-Axion Gravity. For the case of extremal black hole, by imposing the appropriate boundary condition at spatial infinity of the near horizon extremal geometry, the Virasoro algebra of conserved charges associated with the asymptotic symmetry group is obtained. It is shown that the microscopic entropy of the dual conformal field given by Cardy formula exactly agrees with Bekenstein-Hawking entropy of extremal black hole. Then, by rewriting the wave equation of massless scalar field with sufficient low energy as the SLL(2, R) x SLR(2, R) Casimir operator, we find the hidden conformal symmetry of the non-extremal linear dilaton black hole, which implies that the non-extremal rotating linear dilaton black hole is holographically dual to a two dimensional conformal field theory with the non-zero left and right temperatures. Furthermore, it is shown that the entropy of non-extremal black hole can be reproduced by using Cardy formula.