This book constitutes the refereed proceedings of the Second International XML Database Symposium, XSym 2004, held in Toronto, Canada in August 2004 in association with VLDB 2004. The 15 revised full papers presented were carefully reviewed and selected from around 60 submissions. The papers are organized in topical sections on Xquery processing, searching, ranking, and mapping XML documents; XML constraints checking and correcting; XML processing; and clustering, indexing, and statistics.