Secure XML keyword search based on compression policies

User has to execute the restricted query while XML document with the sensitive information is in the process of transmission or exchange in Internet,it is always the research topic about how to enhance query efficiency and protect the security of sensitive information.Based on the instance information tree with access control policies,extracting the main information’s policies,reversing to act on the instance information tree and saving the special node policy,this method with compacted policies provides important basis for secure and efficient XML Key words query,in addition,it adopts the extensible Dewey coding which makes the query easy.The experimental results show that the algorithms can lighten the burden of storage and improve the efficiency.