PODS

This volume contains the proceedings of the Twenty-third ACM SIGMOD-SIGACT-SIGART Symposium on Principles of Database Systems (PODS 2004), held at Le Maison de la Chimie, Paris, France, on June 14-16, 2004 in conjunction with the 2004 ACM SIGMOD International Conference on Management of Data. It consists of a paper based on the invited talk by Georg Gottlob, and 30 contributed papers that were selected by the program committee for presentation at the symposium.The program committee has selected the contributed papers from 183 submissions. Some of the papers are \extended abstracts" and are preliminary reports on work in progress. While the program committee has read them carefully and discussed them intensively, they have not been formally refereed. It is expected that much of the research described in these papers will be published in detail in computer science journals, where they will go through a formal review.The program committee selected Conditional XPath, the First Order Complete XPath Dialect by Maarten Marx for both the PODS 2004 Best Paper Award and the Best Newcomer Award. Warmest congratulations to the author.The year 2004 marks the first time when the SIGMOD/PODS event was located outside of North America. This recognizes the international status of the event, and will hopefully start a beautiful new tradition.