SIGMOD/PODS'06 PODS 2006 : proceedings of the Twenty-Fifth ACM SIGMOD-SIGACT-SIGART Symposium on Principles of Database Systems, Chicago, Illinois, June 26-28, 2006 ; SIGMOD 2006 : proceedings of the ACM SIGMOD International Conference on Management of Data, Chicago, Illinois, June 27-29, 2006 (Association for Computing Machinery, 2006)