This book constitutes the refereed proceedings of the First International XML Database Symposium, XSym 2003, held in Berlin, Germany in September 2003.
The 18 revised full papers presented were carefully reviewed and selected from 65 submissions. The papers are organized in topical sections on XML-relational database management systems, XML query processing, systems and tools for XML data processing, XML access structures, stream processing and updates, and design issues.
Beginning in 1999, the database research literature has seen an explosion of publications with the goal of using an RDBMS to store and/or query XML data. The problems addressed and solved in this area are diverse. Some publications deal with using an RDBMS to store XML data; others deal with exporting existing relational data in an XML view. The papers use a wide variety of XML query languages, including subsets of XQuery, XML-QL, XPath, and even “oneoff” new proposals; they use a wide variety of languages or ad-hoc constructs to map between the relational and XML schema; and they differ widely in what they “push to SQL” and what they evaluate in middleware.
This diversity renders it difficult to know how the various results presented fit together, and even makes it hard to know what if any open problems remain. As a first step to rectifying this situation, we present a classification of the problem space and discuss how almost 40 papers fit into this classification. As a result of this study, we find that some basic questions are still open. In particular, for the XML publishing of relational data and for “schema-based” shredding of XML documents into relations, there is no published algorithm for translating even simple path expression queries (with the // axis) into SQL when the XML schema is recursive. It is our hope that this paper will stimulate others to refine our classification and, more importantly, to improve the state of the art and to address and solve the open problems that the classification reveals.