DATA MODELLING FOR OLAP

Dimensional modelling is primarily to support OLAP and decision making .

Four types of operations are used in OLAP to analyse data. Considering granularity, the operations of drill down and roll up are performed. To browse along the dimensions, slice and dice operations are used.

7.4.1 DRILL DOWN AND ROLL UP

Drill down and roll up are the operations for moving the view down and up along the dimensional hierarchy levels. With drill-down capability, users can navigate to higher levels of detail. With roll-up capability, users can zoom out to see a summarise level of data. The
navigation path is determined by the hierarchies within dimensions.

7.4.2 SLICE AND DICE

Slice and dice are the operations for browsing the data through the visualised cube. Slicing cuts through the cube so that users can focus on some specific perspectives. Dicing rotates the cube to another perspective so that users can be more specific with the data analysis. For example suppose we are considering a company’s production of two products Cell phones and pagers. The dimensions would be location, time, product. While analysing the production report of a specific month by plant and product, you get the quarterly view of gross production by plant. You can then change the dimension from product to time, which is dicing. Now, you want to focus on the Cell Phone only, rather than gross production. To do this, you can cut off the cube only for the Cell Phone for the same dimensions, which is slicing.