---

3. Different OLAP Operations

OLAP allows users to navigate the lattice of cuboids. Here are the primary operations:

3.1 Roll-up (Drill-up)

• Definition: Moving from a lower level of detail to a higher level of detail (summarization).
• Mechanism: Climbing up the concept hierarchy or reducing a dimension.
• Example: Moving from "Sales by City" to "Sales by Country" or summarizing "Daily Sales" to "Monthly Sales".
• Effect: Data is aggregated; detail is lost; volume decreases.

3.2 Drill-down

• Definition: Moving from a higher level of detail to a lower level (more detail).
• Mechanism: Stepping down the concept hierarchy or adding a new dimension.
• Example: Moving from "Yearly Sales" to "Quarterly Sales" or "Sales by Country" to "Sales by City".
• Effect: Data is decomposed; more detail is revealed; volume increases.

3.3 Slice

• Definition: Performing a selection on one dimension of the given cube.
• Mechanism: Fixing the value of one dimension to create a sub-cube.
• Example: "Sales for all Products in all Regions for the Year 2022 only." (The Time dimension is sliced to '2022').
• Result: Reduces the dimensionality of the cube by one.

3.4 Dice

• Definition: Performing a selection on two or more dimensions, creating a sub-cube.
• Mechanism: Defining a range on multiple axes.
• Example: "Sales for 'Electronics' and 'Furniture' (Product) in 'North' and 'South' (Region) for 'Jan' to 'Mar' (Time)."
• Result: A smaller cube defined by specific ranges.

3.5 Pivot (Rotate)

• Definition: Rotating the data axes to view the data from a different perspective.
• Mechanism: Swapping rows and columns.
• Example: Viewing Products on rows and Time on columns, then pivoting to see Time on rows and Regions on columns.
• Use Case: Helps in comparing different dimensions side-by-side.

3.6 Drill-through

• Definition: navigating from a summary cube cell down to the underlying operational data (usually in the source database).
• Example: Seeing that "Sales in Jan were $1M" and drilling through to see the 5,000 individual invoices that made up that total.