---
title: "Define dimension table"
subject: "Data Mining"
chapter: 1
key: "semester_7/data_mining:define-dimension-table"
source: https://www.bctengineer.com/q/semester_7/data_mining/define-dimension-table
site: BCT Engineering
---

# Define dimension table

Data Mining · Chapter 1: Introduction

- Asked in: year not given
- Video: [Fact table and Dimension table | Data Warehousing](https://www.youtube.com/watch?v=dKyA6oBlKwo) — Kishan Mashru
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/data_mining/define-dimension-table
- Whole chapter: https://www.bctengineer.com/md/semester_7/data_mining/chapter-1

## Question

Define Dimension table with example.

## Short answer

A dimension table stores descriptive attributes (e.g., product, time) with a primary key linked to a fact table. It enables filtering and grouping. Example: Item(item_key, item_name, brand, type, supplier) and Time(time_key, day, month, quarter, year).

## Answer

A **dimension table** is a table in a dimensional schema that holds the descriptive attributes about a business entity by which facts are viewed, such as time, product, location or customer. It has a primary key referenced by the fact table and many text attributes, often forming a hierarchy (day, month, quarter, year). It is smaller than the fact table and is used for filtering, grouping and labelling the results.

**Example**: `Item(item_key, item_name, brand, type, supplier)` and `Time(time_key, day, month, quarter, year)`. A query such as "total sales by brand in 2025" uses the dimensions Item and Time to group and filter the facts.

## Check yourself

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

1. What does a dimension table hold?
   A. Backups
   B. Foreign keys only
   C. Numeric measures
   D. Descriptive attributes about entities such as time, product, location
   Answer: D. Dimensions describe what facts are viewed by. (Key point: Dimension content)

2. Which hierarchy fits the Time dimension?
   A. city, name
   B. day, month, quarter, year
   C. brand, type
   D. key only
   Answer: B. Dimensions often form hierarchies. (Key point: Hierarchy)

3. Compared with the fact table, a dimension table is?
   A. Larger and used for measures
   B. Identical
   C. Without keys
   D. Smaller and used for filtering, grouping and labelling
   Answer: D. It has a primary key referenced by the fact table. (Key point: Size and use)

## Related in Data Mining

- [OLAP vs OLTP; OLAP operations, fact, dimension](https://www.bctengineer.com/question.md?key=semester_7%2Fdata_mining%3Aolap-oltp-operations-fact-dimension) — Data Mining, chapter 2
- [OLAP vs OLTP; schema, fact, dimension](https://www.bctengineer.com/question.md?key=semester_7%2Fdata_mining%3Aolap-oltp-schema-fact-dimension) — Data Mining, chapter 2