The Information Management Systems group at the University of Padua, led by Maristella Agosti, has been a major contributor to information retrieval and digital libraries for nearly twenty years.This group has produced some of Italy’s best-known IR researchers, whose work spans a broad range of topics, as the papers in this book demonstrate. One of the goalsof the IR book series is to highlight the work of academic research centers in our field, in order to balancetheperceptionthateveryoneinIRworksforasearchenginecompany. One of the best aspects of our field is that, as academic researchers, we can work with new graduate students and collaborate with companies to ensure that our research has direct impact on systems that people use every day. The Padua group is typical in this respect, and has been involved in a series of collaborations and major European projects over the years. I hope this volume inspires graduate students to pursue research in IR, and I encourage other research groups to contribute their own collections of papers. Amherst, Massachusetts. July 2007. W. Bruce Croft Preface The Information Management Systems (IMS) Research Group was formed in the Department of Information Engineering (formerly Department of El- tronicsandComputer Science)of the UniversityofPadua,Italy,in1987when the department was established. The group activities are concerned with the design,modelingandimplementationofadvancedinformationretrievaltools– such as search engines – and digital library systems.