DATA CUBE

This operator was proposed in Gray et al. (1997), and, subsequently in Gyssens & Lakshamanan (1997) and in Nguyen, Tjoa, & Wagner (2000).

The traditional group-by can generate the core of the n--dimensional data cube. The n-1 lower-dimensional aggregates appear as points (0-D), lines (1-D), planes (2-D), cubes (3-D), or hyper-cubes hanging off the data cube core.

The data cube operator builds a table containing all these aggregate values. The total aggregate using function f( ) is represented as the tuple: ALL, ALL, ALL, …, ALL, f(∗). Points in higher dimensional planes or cubes have fewer ALL values. Then, the cube operator is the n-dimensional generalization of simple aggregate functions. These concepts were represented in the Figure 2.

As discussed in Gray et al. (1997), creating a data cube requires generating the power set of the aggregation columns. Since the cube is an aggregation operation, it makes sense to externalize it by overloading the SQL group-by operator. Figure 21 (taken from Gray et al., 1997) includes an example of the cube syntax.