The Web has brought fundamentally new challenges to data management. Web data management differs from traditional database management in a number of ways. First, Web data differ in their structure: trees with links (usually described by mark-up languages such as XML) instead of tables. Also, Web data are by nature distributed, often on a large number of autonomous servers. Finally, Web data are typically very dynamic and imprecise.

Unlike for the classical relational database model, there is still no commonly accepted model for data management over the Web. The lack of a clean, simple, mathematical model further prevents us from designing general solutions to typical data management problems, such as building indexes, optimizing queries, and guaranteeing certain properties of applications.

As witnessed by the two seminars that previously occurred in Dagstuhl on this topic (Seminar 01361 in 2001 and Seminar 05061 in 2005, both entitled "Foundations of Semistructured Data"), most of the recent research efforts have concentrated on adapting traditional database techniques to the XML setting. In particular, foundational research on XML focused on the tree structure of XML documents, applying well-developed techniques based on logic and automata for trees. These lines of research have been very successful. However, they do not address all the facets of Web data. In particular distribution, dynamicity, incompleteness and reliability had received limited attention in past work, but play a central role in a Web setting. The aim of Seminar 11421 was to bring together researchers covering this spectrum of relevant areas, to report on recent progress in terms of both results as well as new, relevant research questions. It was organized at the initiative of members of the EU funded research projects FoX (fox7.eu) and Webdam (webdam.inria.fr) that are acknowledged for their support.

The workshop brought together 51 researchers from complementary areas of database theory, logic, and theoretical computer science in general, all with an established record of excellence in Web data management. The participant pool comprised both senior and junior researchers, including several advanced PhD students.

Participants were invited to present their own work, and/or survey state-of-the-art advances and challenges in the field. Thirty-four talks were given, which included four (60-90 minute) tutorials and thirty regular (30 minute) talks. All presentations were scheduled prior to the workshop, and due to the flood of volunteered talks, the organizers had to cap the number of slots. Talks were chosen so as to represent well the aspects of Web data management described above. The talks are listed below, classified by the covered topics. The classification is necessarily rough, as many talks crossed the boundaries between areas, in keeping with the seminar's intent. To the organizers' pleasant surprise, some of the results established surprising bridges between fields previously seen as unrelated (such as Machine Learning and Data Exchange), and brought in techniques from novel areas (such as Nominal Sets).

Due to the rich coverage of the area of foundations of Web data management, as achieved by both the presentations and the informal interactions, the organizers regard the seminar as a great success. The weeklong format was well-suited to such an ambitious topic. The topic was well-received, as witnessed by the high rate of accepted invitations, and the exemplary degree of involvement by the paricipants. These volunteered such a high number of exceptional-quality talks that the organizers were faced with not being able to accommodate demand. Bringing together researchers from different areas of data management, programming languages, theoretical computer science and logic fostered valuable interactions and led to fruitful collaborations, as reflected also by the very positive feedback from the audience. The organizers wish to express their gratitude toward the Scientific Directorate of the Center for its support of this seminar, and hope to continue this seminar series on Web data management.