From the Inside Flap FROM THE PREFACE TO THE THIRD EDITION. It has been almost twenty years since the first edition of this book appeared, and ten years since we released the second edition. As one can imagine, in a fast changing area such as this, there have been significant changes in the intervening period. Distributed data management went from a potentially significant technology to one that is common place. The advent of the Internet and the World Wide Web have certainly changed the way we typically look at distribution. The emergence in recent years of different forms of distributed computing, exemplified by data streams and cloud computing, has regenerated interest in distributed data management. Thus, it was time for a major revision of the material. We started to work on this edition five years ago, and it has taken quite a while to complete the work. The end result, however, is a book that has been heavily revised -- while we maintained and updated the core chapters, we have also added new ones. The major changes are the following:Database integration and querying is now treated in much more detail, reflecting the attention these topics have received in the community in the past decade. Chapter 4 focuses on the integration process, while Chapter 9 discusses querying over multidatabase systems. The previous editions had only brief discussion of data replication protocols. This topic is now covered in a separate chapter (Chapter 13) where we provide an in-depth discussion of the protocols and how they can be integrated with transaction management.Peer-to-peer data management is discussed in depth in Chapter 16. These systems have become an important and interesting architectural alternative to classical distributed database systems. Although the early distributed database systems architectures followed the peer-to-peer paradigm, the modern incarnation of these systems have fundamentally different characteristics, so they deserve in-depth discussion in