This revised and expanded edition of Encyclopedia of Database Systems provides easy access to crucial concepts relevant to all aspects of very large databases, data management, and database systems, including areas of current interest and research results of historical significance. This comprehensive reference is organized alphabetically and each entry presents basic terminology, concepts, methods and algorithms, key results to date, references to the literature, and cross-references to other entries. Topics for the encyclopedia -- including areas of current interest as well as research results of historical significance -- were selected by a distinguished international advisory board and written by world-class experts in the field. New entries that reflect recent developments and technological advances in very large databases include: big data, big data technology, cloud computing, cloud data centers, business analytics, social networks, ranking, trust management, query over encrypted data, and more. Entirely new entries include database systems, relational database systems, databases, multimedia databases, bioinformatics, workflow systems, and web data management. Encyclopedia of Database Systems, 2nd edition, is designed to meet the needs of researchers, professors, graduate and undergraduate students in computer science and engineering. Industry professionals, from database specialists to software developers, will also benefit from this valuable reference work.