An enterprise data-warehouse architecture needs to be as flexible as possible to meet the entire spectrum of current and future requirements. To maximize flexibility, a consolidated data warehouse should be stored in a standard RDBMS with a normalized database design, with some summaries and denormalization added for performance. This kind of data-warehouse design is sometimes called an atomic data warehouse.
The main purposes of an atomic data warehouse are to serve as a staging ground for subsets of the atomic warehouse, called data marts, and to serve as a reference data warehouse. The size, central location, and database design of the atomic warehouse may not be suitable to the varied needs of particular groups. These data marts are copied to other computers as data warehouses in their own right.
Data marts may be as large as (or even larger than) the data warehouse that spawned them. They may be located near the atomic warehouse or distributed close to the users. This placement depends on use and communications costs.
Data marts are data warehouses built to meet particular user needs. They may be hundreds of gigabytes in size. But it is their focus, not their size, that makes them data marts.
For example, users in France may care only about data that pertains to them and would prefer to work only with that geographical subset. A department might be interested just in particular customers and so would want only that subject subset. A group analyzing profitability might best be supported by a dimensional structure, so the organization would set up a data mart with the data structures and summaries appropriate for multidimensional analysis for them.
These data marts can be built with four kinds of RDBMSs:.
First, a traditional relational database can be used for standard queries and analysis. A wide spectrum of tools such as those from Brio, Business Objects, or Cognos can retrieve and manipulate this kind of data.