An OLAP Cube is a data structure that allows fast analysis of data according to the multiple Dimensions that define a business problem. A multidimensional cube for reporting sales might be, for example, composed of 7 Dimensions: Salesperson, Sales Amount, Region, Product, Region, Month, Year.
Basic analytical operations of OLAP
There are four types of OLAP Operations:
- Roll-up
- Drill-down
- Slice and dice
- Pivot (rotate)
1. Roll-Up:
Roll-up is also known as “consolidation” or “aggregation.” The Roll-up operation can be performed in 2 ways
- Reducing dimensions
- Climbing up concept hierarchy. Concept hierarchy is a system of grouping things based on their order or level.
In this cube, the roll-up operation is performed by climbing up in the concept hierarchy of Location dimension (City -> Country)
2. Drill-down:
In drill-down data is fragmented into smaller parts. It is the opposite of the rollup process. It can be done via
- Moving down the concept hierarchy
- Increasing a dimension
In this cube, the drill down operation is performed by moving down in the concept hierarchy of Time dimension (Quarter -> Month)
3. Slice and dice:
Slice selects a single dimension from the OLAP cube which results in a new sub-cube creation. In the cube given in the overview section, Slice is performed on the dimension Time = “Q1”
Dice selects a sub-cube from the OLAP cube by selecting two or more dimensions. In the cube given in the overview section, a sub-cube is selected by selecting following dimensions with criteria:
- Location=Delhi or Kolkata
- Time = Q1 or Q2
- Item = Car or Bus
4. Pivot:
Pivot is also known as rotation operation as it rotates the current view to get a new view of the representation. In the sub-cube obtained after the slice operation, performing pivot operation gives a new view of it
Types of OLAP systems
- ROLAP
- MOLAP
- HOLAP