Data Mart
What is the difference between a data warehouse and a data mart?
In general a Data Warehouse is used on an enterprise level, while Data Marts is used on a business division/department level. A data mart only contains the required subject specific data for local analysis.
A database, or collection of databases, designed to help managers make strategic decisions about their business. Whereas a data warehouse combines databases across an entire enterprise, data marts are usually smaller and focus on a particular subject or department. Some data marts, called dependent data marts, are subsets of larger data warehouses. A data mart is a simpler form of a data warehouse focused on a single subject (or functional area) such as sales, finance, marketing, HR etc. Data Mart represents data from single business process.
A data mart can run in size from megabytes to gigabytes
Data warehouse may run from gigabytes to Terabytes
Three technologies are needed to generate on-demand data marts:
An accessible meta data repository that users can query.
An extract tool that can get to the data on demand.
A target database management system (DBMS) that can automatically generate a database.
The extract tool should provide access to data in a variety of data sources. Data is typically stored in several places: a data warehouse, operational data stores, operational databases and flat files. Some data stores can be extracted in near-real time, such as a data warehouse. Others have to wait so that key business functions are not disturbed. The extraction should be scheduled automatically, with clear communication to the user of the time schedule. The source should be relatively transparent to the user, while ensuring that the meta data descriptions provide enough context for the user to know that the correct source is being tapped.
To provide easier data analysis, this database should be relational. However, substantial technical expertise is required to design and create a relational database that has acceptable performance characteristics. The major technology advance in this area has been the introduction of databases that permit the effective creation of in-memory databases. In turn, this technology delivers analysis performance without the need for physical database design in the traditional sense. This provides a great solution for the creation of short-lived databases that are needed quickly, but only for limited periods of time.
Each Data Mart may contain several Fact Tables each with many Dimension Tables
