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<p>A group-select operation has been defined for relational algebra. This operation is found to be useful for efficiently reducing expressions of nonprocedural relational languages that permit natural quantifiers. Conceptually, the operation first partitions a relation into blocks of tuples that have the same value for an attribute or attribute concatenation. It then extracts each block for which a specified number of tuples meet a specifiedcondition. The quantity of tuples for the operation is specified by means of a natural quantifier. Performance of the group-select operation will be poor with conventional file processing, making the operation more suitable for use with a database machine with an associative memory.</p>
relational algebra; database machine design; group-select operation; nonprocedural relational languages; natural quantifiers; tuples; associative memory; relational databases

J. Bradley, "A Group-Select Operation for Relational Algebra and Implications for Database Machine Design," in IEEE Transactions on Software Engineering, vol. 14, no. , pp. 126-129, 1988.
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