The design of a data warehouse depends on identifying facts, dimensions, and granularity. Facts are summarized numerical data stored in a table called a fact table. Dimensions are categories by which summarized data can be viewed. Each dimension can have one or more hierarchies. Hierarchies are logical structures that use ordered levels as a means of organizing data. Query tools use hierarchies to drill down or roll up into your retrieved facts to view different levels of granularity. Granularity refers to the level of detail of the data stored in a fact table. The more detail there is in a fact table, the higher its granularity and vice versa.