In many respects, rewriting a book is more difficult than writing it the first time. If the book is successful, as this one is, a major concern is that the updates, inserts, and deletions will adversely affect writing style and continuity of coverage. (The medical profession's guiding principle comes to mind: First, do no harm.) Naturally, our own experience is a good starting point, but we also know that authors can develop a proprietary attitude that prevents them from spotting weaknesses or opportunities for improvement. Fortunately, the efforts of a combination of superb reviewers and editors, in addition to a wealth of feedback from adopters and students of the previous editions, helped provide the proper guidance and evaluation for rewriting This seventh edition continues to provide a solid and practical foundation for the design, implementation, and manage-ment of database systems. This foundation is built on the notion that, while databases are very practical things, their suc cessful creation depends on understanding the important concepts that define them. It's not easy to come up with the proper mix of theory and practice, but we are grateful that the previously mentioned feedback suggests that we largely succeeded in our quest to maintain the proper balance.