DEC 9, 2003 1:00am ET

Related Links

Which CDC method is the best to achieve staging database with changed data?
March 7, 2008
Apart from bloated dimension, what are the negatives of using all known attributes in your SCD?
March 7, 2008
When is it better to have normalized data to create data marts and when is it better to have dimensional data?
March 7, 2008

Web Seminars

Why Data Virtualization Can Save the Data Warehouse
September 17, 2014
Essential Guide to Using Data Virtualization for Big Data Analytics
September 24, 2014

What is a degenerate dimension and how is it used

Print
Reprints
Email

Q:

What is a degenerate dimension and how is it used?

A:

Chuck Kelley’s Answer: A degenerate dimension is data that is dimensional in nature but stored in a fact table. For example, if you have a dimension that only has Order Number and Order Line Number, you would have a 1:1 relationship with the Fact table. Do you want to have two tables with a billion rows or one table with a billion rows. Therefore, this would be a degenerate dimension and Order Number and Order Line Number would be stored in the Fact table.

Joe Oates’ Answer: Many data warehouse transaction fact tables have a control number, such as an invoice number, purchase order number or policy number. Over the course of years reflected in the data warehouse, there could be hundreds of thousands or even millions of each particular control number such as invoice number. It isn’t practical to have a drop-down list of each of these numbers to find data typically found in the legacy system invoice header such as invoice number, invoice date, invoice type. Consequently, these data items are put into the line-item fact table to slice and dice as the users wish. These control numbers are called degenerate dimensions.

If you were to have a dimension table for invoice, you would have nearly as many entries in the dimension table as you have in the line-item fact table. The line-item fact table is generally the largest table by far in the data warehouse. So joining the multimillion or multibillion row fact table to a multimillion or multibillion row dimension table will cause your data warehouse to take up much more disk storage that it should as well as significantly degrading performance

Clay Rehm’s Answer: A degenerate dimension is a dimension that is stored in the fact table rather than the dimension table. It eliminates the need to join to a Dimension table.

Get access to this article and thousands more...

All Information Management articles are archived after 7 days. REGISTER NOW for unlimited access to all recently archived articles, as well as thousands of searchable stories. Registered Members also gain access to:

  • Full access to information-management.com including all searchable archived content
  • Exclusive E-Newsletters delivering the latest headlines to your inbox
  • Access to White Papers, Web Seminars, and Blog Discussions
  • Discounts to upcoming conferences & events
  • Uninterrupted access to all sponsored content, and MORE!

Already Registered?

Filed under:

Advertisement

Comments (0)

Be the first to comment on this post using the section below.

Add Your Comments:
You must be registered to post a comment.
Not Registered?
You must be registered to post a comment. Click here to register.
Already registered? Log in here
Please note you must now log in with your email address and password.
Twitter
Facebook
LinkedIn
Login  |  My Account  |  White Papers  |  Web Seminars  |  Events |  Newsletters |  eBooks
FOLLOW US
Please note you must now log in with your email address and password.