Determine the granularity of the fact table
After you gather all the relevant information about the subject area, the next step in the design process is to determine the granularity of the fact table.
To do this you must decide what an individual low-level record in the fact table should contain. The components that make up the granularity of the fact table correspond directly with the dimensions of the data model. Therefore, when you define the granularity of the fact table, you identify the dimensions of the data model.