---
title: "Define drilling"
subject: "Data Mining"
chapter: 2
key: "semester_7/data_mining:define-drilling"
source: https://www.bctengineer.com/q/semester_7/data_mining/define-drilling
site: BCT Engineering
---

# Define drilling

Data Mining · Chapter 2: Data Pre-processing

- Asked in: year not given
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/data_mining/define-drilling
- Whole chapter: https://www.bctengineer.com/md/semester_7/data_mining/chapter-2

## Question

Define drilling with example.

## Answer

**Drilling** (drill-down) is an OLAP operation that moves from **summarised data to more detailed data**. It is done by stepping down a concept hierarchy (e.g. year → quarter → month → day) or by introducing an additional dimension. The reverse operation is **roll-up (drill-up)**.

**Example**: a report shows sales by quarter: Q1 = 5 lakh. Drilling down on Q1 shows sales for January, February and March separately. Drill-down by adding a dimension would split the same figure by item type.

```text
 Year 2025 -> Q1, Q2, Q3, Q4 -> Jan, Feb, Mar ...
        (drill-down ->)   (<- roll-up)
```

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What is drill-down?
   A. Moving from detail to summary
   B. Moving from summarised data to more detailed data
   C. Selecting one value on a dimension
   D. Removing outliers
   Answer: B. Drill-down goes to finer detail; its reverse is roll-up. (Key point: Drill-down definition)

2. Which is a way to perform drill-down?
   A. Step up a concept hierarchy
   B. Delete a dimension
   C. Step down a concept hierarchy or add a dimension
   D. Apply min-max normalisation
   Answer: C. Drill-down uses a lower hierarchy level (e.g. quarter to month) or an extra dimension. (Key point: Ways to drill down)

3. Drilling down on Q1 sales of 5 lakh in a time hierarchy shows what?
   A. Sales for the whole year
   B. Only the Q2 figure
   C. Sales for all quarters combined
   D. Sales for January, February and March
   Answer: D. Quarter steps down to months. (Key point: Drill-down example)