Data Marts Sourced by a Data Warehouse
Many data warehousing experts would argue that a true data mart is a “retail outlet,” and a data warehouse provides its contents, as shown in this figure.
In an environment like the one shown in this figure, the data sources, data warehouse, data mart, and user interact in this way:
The data sources, acting as suppliers of raw materials, send data into the data warehouse.
The data warehouse serves as a consolidation and distribution center, collecting the raw materials in much the same way that any data warehouse does.
Instead of the user (the consumer) going straight to the data warehouse, though, the data warehouse serves as a wholesaler with the premise of “we sell only to retailers, not directly to the public.” In this case, the retailers are the data marts.
The data marts order data from the warehouse and, after stocking the newly acquired information, make it available to consumers (users).
In a variation of the sourced-from-the-warehouse model, the data warehouse that serves as the source for the data mart doesn’t have all the information the data mart’s users need. You can solve this problem in one of two ways:
Supplement the missing information directly into the data warehouse before sending the selected contents to the data mart, as shown in this figure.
Don’t touch the data warehouse; instead, add the supplemental information to the data mart in addition to what it receives from the data warehouse, as shown in this figure.
If your data mart is the only one within your company that needs additional data (be sure to ask around), leave the warehouse alone and bring the supplemental data directly into your data mart.
If other data marts or other projects served by the data warehouse can use the additional information, add that information to the data warehouse first and then send it, along with the other contents you need, to the appropriate data marts.