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Map-Reduce is a programming model that enables easy development of scalable parallel applications to process a vast amount of… Expand This paper introduces RankSQL, a system that provides a systematic and principled framework to support efficient evaluations of… Expand The handling of user preferences is becoming an increasingly important issue in present-day information systems. Among others… Expand The join operation is one of the fundamental relational database query operations. It facilitates the retrieval of information… Expand Abstract Motivated by new applications of database systems we introduce relations which may have relation-valued attributes and… Expand Abstract This paper deals with relational databases which are extended in the sense that fuzzily known values are allowed for… Expand Two complexity measures for query languages are proposed. Data complexity is the complexity of evaluating a query in the language… Expand Aggregate functtons m relattonal query languages allow intricate reports to be written. In this paper aggregate functions are… Expand We present an algorithm for constructing a tree to satisfy a set of lineage constraints on common ancestors. We then apply this… Expand In the near future, we can expect a great variety of languages to be proposed for interrogating and updating data bases. This… Expand