Definition data Warehouse VS database

Very often, the question is asked- what's the difference between a data mart and a data warehouse- which of them do I need?

Data warehouse or Data Mart?

Data Warehouse:

• Holds multiple subject areas
• Holds very detailed information
• Works to integrate all data sources
• Does not necessarily use a dimensional model but feeds dimensional models.

Data Mart

• Often holds only one subject area- for example, Finance, or Sales
• May hold more summarised data (although many hold full detail)
• Concentrates on integrating information from a given subject area or set of source systems
• Is built focused on a dimensional model using a star schema.

More Detail regarding Data Warehouse Vs Datamart: and Inmon vs Kimball

As the concept of decisional systems, and data warehouses and data marts evolved, two major points of view came into existence. There are two giants in this field. Bill Inmon, and Ralph Kimball.

There are some that argue the best approach is to start with data marts, department by department, then merge them together to form a data warehouse- this is more in line with Kimballs approach.

"You can catch all the minnows in the ocean and stack them together and they still do not make a whale, "

Ralph Kimball, on the other hand, advocates what he calls a bus architecture data warehouse. His methodology specifies conformed dimensions, where multiple fact tables share common dimensional tables. For me, each of these fact tables represents a data mart. The row of dimensional tables that all the fact tables plug into is the bus, and because, for example, the finance and the sales data marts both use the same product dimension table there is integration between departments.

The more extreme data mart strategy is that of the completely stand alone data mart, the concept being that its fast, easy, cheap, and delivers value immediately. I'm a supporter of this at the desktop level- thats the point of the Datamartist tool afterall. But I don't buy this for server based architectures- what is really fast, easy and cheap when you have to buy servers, create a project and form a commitee? In my mind if you've decided you need a central server solution, some level of integration is needed, and don't pretend its going to be magic.