A typical three level architecture adds data marts to the generic architecture. The data marts are subsets of the data warehouse, designed to meet the decision-making needs of a specific set of users. EDW and Data Mart server different purposes and have different data structures. Transforming data is two-step process. Data marts are customized for each set of users.
Operational data is stored in transaction systems.
Derived data is stored in each Data Mart. The data associated with the EDW is reconciled data. A variety of functions may be performed on the data. The reconciled data in the EDW is the source for the reconciled data layer used by the data marts. Grain granularity of data Market basket analysis analysis of individual customers.