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 be useful for very efficiently reducing expressions of non procedural 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 data base machine with an associative memory.