Cardinality Constraints for XML: Challenging the Trade-off between Expressiveness and Tractability 2. IDENTIFICATION Contact Principal Investigator Name (with title): Associate Professor Sebastian Link Full Address: School of Information Management

Describe in up to 200 words the nature of your proposed research in plain English for a general audience. This summary should be able to be used for publicity purposes if the proposal is offered funding. The eXtensible Markup Language (XML) has evolved to be the " lingua franca " for data integration and data exchange on the Internet and elsewhere. This development has led to a dramatic increase of XML data that must be stored, managed and processed in its native format. The syntactic flexibility of XML together with the tree-like nested structure of its data impose new challenges for database researchers. It is particularly difficult to develop data management tools that are both efficient and cater for a large class of properties that are naturally exhibited by XML data. Our project is based on the somewhat surprising observation that cardinality constraints have not been exploited in the context of XML. Cardinality constraints can express many properties of XML data that cannot be captured by other classes of XML constraints. They have a direct impact on many XML recommendations such as schema specification languages, query languages or data manipulation and transformation languages. We aim at developing a well-founded theory that gives original insight into the characteristics of XML data, enhances the semantic capabilites of XML, allows designers to make an informed choice about which classes of cardinality constraints to incorporate into XML recommendations, and provides efficient algorithms to advance XML data processing.