A Group-Select Operation for Relational Algebra and Implications for Database Machine Design.

A group-select operation has been defined for relational algebra. This operation is found to lie 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 specified condition. 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. [ABSTRACT FROM AUTHOR]