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XPath queries are usually translated into an algebra that combines traditional relational operators and XML-specific ones. In particular, FLWOR loops are represented using nest, unnest, join, and similar operators and their original nested-loop nature disappears, creating an opportunity for bulk evaluation and join reordering. In XQuery, two additional issues shall be handled -- tree construction and the presence of user-defined functions. The recursive nature of functions pushes the problem outside of the range of relational algebra. This book presents a novel evaluation framework based on an expanding network of relational operators, called R-program. In this environment, functions are evaluated in bulk instead of evaluating each call separately. Besides obvious advantages of bulk evaluation, R-programs also allow rearrangement of data flow across function boundaries. A set of program transformations employing these capabilities is described; together with rule-based static interprocedural analysis algorithms used to determine the applicability of the transformations.
About the author
David Bednárek received his Master's degree in Informatics from Charles University in Prague in 1991. After a decade in education and business, he returned to research at his alma mater and received his Ph.D. in 2009. His research interests include programming languages, compiler construction, parallel programming, and database systems.
