This book is an anthology of the results of research and development in database query processing during the past decade. The relational model of data provided tremendous impetus for research into query processing. Since a relational query does not specify access paths to the stored data, the database management system (DBMS) must provide an intelligent query-processing subsystem which will evaluate a number of potentially efficient strategies for processing the query and select the one that optimizes a given performance measure. The degree of sophistication of this subsystem, often called the optimizer, critically affects the performance of the DBMS. Research into query processing thus started has taken off in several directions during the past decade. The emergence of research into distributed databases has enormously complicated the tasks of the optimizer. In a distributed environment, the database may be partitioned into horizontal or vertical fragments of relations. Replicas of the fragments may be stored in different sites of a network and even migrate to other sites. The measure of performance of a query in a distributed system must include the communication cost between sites. To minimize communication costs for-queries involving multiple relations across multiple sites, optimizers may also have to consider semi-join techniques.

Traditionally, the primary cocaine trafficking routes from South America started at coca farms and laboratories in Colombia, traversed Mexico and the Caribbean, and ended with dealers and users in the US. In the last decade, a significant shift has occurred, with increasing amounts of cocaine travelling through West Africa to Europe. This shift developed in response to increased cocaine demand in Europe, successful interdiction of traditional trafficking routes in the Western Hemisphere, and weak governance in West Africa. However, the significance of this shift in narcotrafficking patterns goes far beyond opening a new front in the "War on Drugs." The hybridization of profit-motivated transnational organized criminal groups with ideologically-driven international terrorist networks threatens to accelerate the destabilization of the nations of West Africa while generating significant funding for terrorist groups.