Hui Wang Divesh Srivastava Laks V. S. Lakshmanan SungRan Cho Sihem Amer-Yahia Optimizing Tree Pattern Queries over Secure XML Databases. 127-165 2007 Secure Data Management in Decentralized Systems http://dx.doi.org/10.1007/978-0-387-27696-0_5 series/ais/33 db/series/ais/ais33.html#WangSLCA07