 <p>The denormalization is in the dimension tables in a star schema: E. g. in a product table, you explicitly have many columns like several levels of product category in this one table, instead of having one table for each level, and using foreign keys referencing those values.</p> <p>This means you have normalization with regard to facts, but stop normalizing on the dimension tables.</p> <p>Furthermore, you often do not even completely denormalize the facts. A typical example would be this: in a completely normalized table, you would use only two columns 'number of units sold' and 'price per unit', but in an OLAP database, it may make sense to redundantly have another column for the 'sales value' which could easily be calculated by multiplying units sold and the price per unit.</p>