Layer 3: Data Stores
An operational data store (ODS) is a database designed to integrate data from multiple sources to make analysis and reporting easier. Because the data originates from multiple sources, the integration often involves cleaning, resolving redundancy and checking against business rules for integrity. An ODS is usually designed to contain low level or atomic (indivisible) data (such as transactions and prices) with limited history that is captured "real time" or "near real time" as opposed to the much greater volumes of data stored in the data warehouse generally on a less frequent basis.
Data mart (DM) is a subset of an organizational data store, usually oriented to a specific purpose or major data subject that may be distributed to support business needs. DM is analytical data stores designed to focus on specific business functions for a specific community within an organization. Data marts are often derived from subsets of data in a data warehouse, though in the bottom-up data warehouse design methodology the data warehouse is created from the union of organizational data marts.