Relational schema mappings have been extensively studied in connection with data integration and exchange
problems, but mappings between XML schemas have not received the same amount of attention. Our goal
is to develop a theory of expressive XML schema mappings. Such mappings should be able to use various
forms of navigation in a document, and specify conditions on data values. We develop a language for XML
schema mappings, and study both data exchange with such mappings and metadata management problems.
Specifically, we concentrate on four types of problems: complexity of mappings, query answering, consistency
issues, and composition.