Recently, we have seen steep increase in popularity and adoption of XML, in areas such as traditional databases, e-business, the scientific environment, and on the web. Quering XML documents and data efficiently is a challenging issue; this book approaches search on XML data by combining content-based methods from information retrieval and structure-based XML query methods and presents the following parts: applications, query languages, retrieval models, implementing intelligent XML systems, and evaluation. To appreciate the book, basic knowledge of traditional database technology, information retrieval, and XML is needed. The book is ideally suited for courses or seminars at the graduate level as well as for angoing education of research and development professionals working on Web applications, digital libraries, database systems, and information retrieval.