This book tackles the problems of update algorithms for databases. How can one construct and maintain a database of facts, capable of incorporating new information and getting rid of all outdated information, and yet in the process not disturb any other information in the database? The author has produced a formal method of specifying the desired change intentionally using a "formula-based" approach to updating needs rather than a "model-based" technique. The complexity of the algorithms, choice of semantics and means of enforcing integrity constraints are also discussed.