The use of logic in databases started in the late 1960s. In the early 1970s Codd formalized databases in terms of the relational calculus and the relational algebra. A major influence on the use of logic in databases was the development of the field of logic programming. Logic provides a convenient formalism for studying classical database problems and has the important property of being declarative, that is, it allows one to express what she wants rather than how to get it. For a long time, relational calculus and algebra were considered the relational database languages. However, there are simple operations, such as computing the transitive closure of a graph, which cannot be expressed with these languages. Datalog is a declarative query language for relational databases based on the logic programming paradigm. One of the peculiarities that distinguishes Datalog from query languages like relational algebra and calculus is recursion, which gives Datalog the capability to express queries like computing a graph transitive closure. Recent years have witnessed a revival of interest in Datalog in a variety of emerging application domains such as data integration, information extraction, networking, program analysis, security, cloud computing, ontology reasoning, and many others. The aim of this book is to present the basics of Datalog, some of its extensions, and recent applications to different domains.

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Sergio Greco is a Full Professor and Chair of the DIMES Department at the University of Calabria (Italy). Before that he was Assistant Professor (1989-1998) and Associate Professor (1998-2000) at the University of Calabria and visiting researcher at the Microelectronics and Computer Corporation of Austin (1990-1991) and at the of University of California at Los Angeles (1996 and 1998). Prof. Greco's research interests include database theory, data integration, inconsistent data, data mining, knowledge representation, logic programming, and computational logic. Cristian Molinaro received his Ph.D. degree in Computer Science Engineering from the University of Calabria, Italy. He was a Visiting Scholar at the Department of Computer Science and Engineering of the State University of New York at Buffalo. He was a Faculty Research Assistant at the University of Maryland Institute for Advanced Computer Studies (2009-2011). Currently, he is an Assistant Professor at the University of Calabria,Italy. His research interests include database theory and logic programming.