What is a OLAP Cube ?

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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:

  1. Roll-up
  2. Drill-down
  3. Slice and dice
  4. Pivot (rotate)

1. Roll-Up:

Roll-up is also known as “consolidation” or “aggregation.” The Roll-up operation can be performed in 2 ways

  1. Reducing dimensions
  2. 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

  1. ROLAP
  2. MOLAP
  3. HOLAP