

This operator was defined in Klug (1982) and subsequently in Ozsoyoglu, Ozsoyoglu, & Matos (1987).
The aggregate formation operator first partitions tuples of relation R such that tuples having the same X component are in the same partition. Then the function f is applied to component A of tuples in each partition, and the Xvalue and the associated aggregate value are output for each partition.
Let be a relation included in the set of relations in the database, with Let be an aggregate function and A be simplevalued, with A ∊ Atr (R). Then, is a relation with degree k+1 and is defined as
where ‘o’ denotes concatenation.

