Functional Dependencies in Controlling Sparsity of OLAP Cubes

We will study how relational dependency information can be applied to OLAP cube design. We use dependency information to control sparsity, since functional dependencies between dimensions clearly increase sparsity. Our method helps the user in finding dimensions and hierarchies, identifying sparsity risks, and finally changing the design in order to get a more suitable result. Sparse raw data, a large amount of pre-calculated aggregations, and many dimensions may expand the need of the storage space so rapidly that the problem cannot be solved by increasing the capacity of the system. We give two methods to construct suitable OLAP cubes. In the synthesis method, attributes are divided into equivalence classes according to dependencies in which they participate. Each equivalence class may form a dimension. The decomposition method is applied when candidates for dimensions exist. We decompose dimensions based on conflicts, and construct new cubes for removed dimensions until no conflicts between dimensions exist.