Proceedings of the twenty-first ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems

This volume contains the proceedings of the Twenty-Sixth ACM SIGMOD-SIGACT-SIGART Symposium on Principles of Database Systems (PODS 2007), held in Beijing, China, on June 11-13, 2007, in conjunction with the 2007 ACM SIGMOD International Conference on Management of Data. The proceedings include papers based on the keynote address by Dan Suciu and two invited tutorials by Nicole Schweikardt and Jan Van den Bussche, and 28 contributed papers that were selected by the Program Committee from 187 submissions. Most of these papers are extended abstracts and, while they have been read by the program committee, they have not been formally refereed. It is anticipated that many of them will appear in more polished form in scientific journals. The program committee selected the paper "Generalized Hypertree Decompositions: NP-Hardness and Tractable Variants" by Georg Gottlob, Zoltan Miklos and Thomas Schwentick as the recipient of the Best Paper Award, and the paper "XML Transformation by Tree-Walking Transducers with Invisible Pebbles" by Joost Engelfriet, Hendrik Jan Hoogeboom and Bart Samwel as the recipient of the Best Newcomer Award. Warmest congratulations to the authors. I thank all authors who submitted papers to the conference, and the members of the program committee for the enormous amount of work they have done. The program committee did not meet in person, but carried out extensive discussion during the electronic PC meeting.