Chapter 9. Dimension Table Core Concepts
Building on your solid understanding of fact tables from Chapter 8, it's time to turn your attention to dimension tables, whose descriptive attributes allow the business users to filter and group information in nearly countless ways. Robust dimension tables filled with interesting attributes enable robust analytics.
The chapter begins by discussing the importance of replacing a dimension's natural operational keys with meaningless integer surrogate keys during the ETL process. From that basic concept, the second section focuses on the time (or date) dimension that you'll find with virtually every fact table.
We then describe other common dimension table patterns, including role-playing, junk, and causal dimensions. We close out the chapter with a deep dive into techniques for handling slowly changing dimension (SCD) attributes.
There are lots of additional topics to discuss when it comes to dimensions; hang onto your hats for more coverage in Chapter 10.
Dimension Table Keys
The first two articles in this chapter focus on the value of using meaningless surrogate keys as the primary keys of your dimension tables.
9.1 Surrogate Keys
Ralph Kimball, DBMS, May 1998
According to the Webster's Unabridged Dictionary, a surrogate is an "artificial or synthetic product that is used as a substitute for a natural product." That's a great definition for the surrogate ...