The topic of using views to answer queries has been popular for a few decades now, as it cuts across domains such as query optimization, information integration, data warehousing, website design and, recently, database-as-a-service and data placement in cloud systems.

This book assembles foundational work on answering queries using views in a self-contained manner, with an effort to choose material that constitutes the backbone of the research. It presents efficient algorithms and covers the following problems: query containment; rewriting queries using views in various logical languages; equivalent rewritings and maximally contained rewritings; and computing certain answers in the data-integration and data-exchange settings. Query languages that are considered are fragments of SQL, in particular select-project-join queries, also called conjunctive queries (with or without arithmetic comparisons or negation), and aggregate SQL queries.

This second edition includes two new chapters that refer to tree-like data and respective query languages. Chapter 8 presents the data model for XML documents and the XPath query language, and Chapter 9 provides a theoretical presentation of tree-like data model and query language where the tuples of a relation share a tree-structured schema for that relation and the query language is a dialect of SQL with evaluation techniques appropriately modified to fit the richer schema.

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Foto N. Afrati is a professor in the Electrical and Computing Engineering Department of the NTUA, Greece. She received a B.S. degree from the Mechanical and Electrical Engineering Department of National Technical University of Athens (NTUA) and a Ph.D. from Imperial College of the University of London. She is a Fellow of ACM. She has received the ACM Recognition for Service Award in 2005 and the best-paper award in ICDT 2009. She has been the program-committee chair for the Conference on Principles of Databases (PODS) 2005, and for the International Conference on Database Theory (ICDT) 1997, for which she was the organizing committee chair as well. She currently serves as associate editor of the IEEE TKDE journal. In 2012-2013, she spent her sabbatical leave visiting Google at Mountain View. She has published over 100 papers in the areas of databases, algorithms, and distributed computing. Her research interests are in the area of database theory, recent research interests are mainly in the area of big data, including query optimization for MapReduce and other distributed platforms.Rada Y. Chirkova is an associate professor of Computer Science at North Carolina State University. She has received a B.Sc. and a M.Sc., both in Applied Mathematics, from Moscow State University (Moscow, Russia), and an M.Sc. and a Ph.D., both in Computer Science, from Stanford University. She is a senior member of the Association for Computing Machinery, and served in 2017 as General Co-Chair of the ACM International Conference on Management of Data (SIGMOD). She is associate editor of the SIGMOD Record journal and of The Computer Journal (Oxford). She has co-authored 3 books (including this book), and has over 60 peer-reviewed publications on topics ranging from query containment and equivalence, query processing, view-based reformulation of data and queries, information security and leakage, to applications of policies to agent behaviors. She has received the National Science Foundation (NSF) CAREER Award, as well as numerous IBM Faculty and University Partnership Program Awards. Her research interests span information and knowledge management, algorithms and theory of computation, and data sciences and analytics, with applications including data wrangling, cyber security, and healthcare information technology.