Chapter 8. Dimension Tables

In the last chapter, we examined fact tables, the relation that sits at the core of every star schema. In this chapter, we'll examine the other type of table found in dimensional databases, the dimension table from which, of course, the model takes its name.

In some respects, dimension tables are similar to the look-up tables common to normalized databases, but despite their surface resemblance, dimension tables serve an entirely different purpose. Look-up tables are intended to reduce duplicate data and ensure consistency. Dimension tables represent the characteristics that are being measuredit is at the conjunction of a set of dimension values that a measurement is taken. Although dimension tables can, as a side effect, reduce the size of the fact table and the amount of duplicate data it contains, their primary purpose is to facilitate analysis. They are the means by which analysts drill down through masses of data.