Invited Talks -- Normalization Theory for XML -- Dynamic Fusion of Web Data -- XPath Query Answering -- XPath Query Satisfiability is in PTIME for Real-World DTDs -- Fast Answering of XPath Query Workloads on Web Collections -- XQuery Evaluation and Performance -- Let a Single FLWOR Bloom -- Efficient XQuery Evaluation of Grouping Conditions with Duplicate Removals -- On the Effectiveness of Flexible Querying Heuristics for XML Data -- XML Updates, Temporal XML Data and Concurrency -- XML Schema Evolution: Incremental Validation and Efficient Document Adaptation -- Managing Branch Versioning in Versioned/Temporal XML Documents -- SXDGL: Snapshot Based Concurrency Control Protocol for XML Data -- Panel -- The Generation Y of XML Schema Matching Panel Description.

Since its first edition in 2003, the XML Database Symposium series (XSym) has been a forum for academics, practitioners, users and vendors to discuss the use of and synergy between databases and XML. The previous symposia have provided opportunities for timely discussions on a broad range of topics pertaining to the theory and practice of XML data management and its applications. XSym 2007 continues this tradition with a program consisting of three research sessions, two keynote talks and a panel. We received 28 full paper submissions, out of which 8 were accepted for publication in these proceedings. Each submitted paper underwent a rigorous and careful review by a minimum of 4 independent referees. The contributions in these proceedings are a fine sample of the very best current research in XPath and XQuery processing, XML Updates, Temporal XML and Constraints. This volume also contains two invited short papers by the XSym 2007 keynote speakers: Leonid Libkin (University of Edinburgh, UK) contributed a thorough discussion of Normalization Theory for XML, while Erhard Rahm (University of Leipzig, Germany) contributed an interesting overview of the work on Dynamic Fusion of Web Data carried out at his - search group. This year, XSym will top its program off by an exciting panel with the title "The Generation Y of XML Schema Matching". It was proposed and is organized by Avigdor Gal from Technion - Israel Institute of Techn- ogy.