A centralized data repository designed with enterprise-wide usage in mind. Data warehouse provides facility for getting quick, accurate, and often insightful information. A Data Warehouse is designed so that its users can recognize the information they want and access that information using simple tools. A Data Warehouse integrates operational data from various sources into a single and consistent architecture that supports analysis and decision-making within the organization.
Data warehouses may consist of large amount of data, sometimes in smaller logical units called Data marts. Often the schemas of data marts are stored in what are known as “star schemas”, or dimensional modeling form; however there is no industry standard requiring that the schemas of data marts be in any particular form. Data warehouses are usually accessed (queried) via “data marts”, which are purpose-specific access points to or sub-sets of the warehouse. Data marts are designed to answer the probable queries of a given kind of user.
Data warehousing Approaches:-
With Data Warehousing we have two schools of thought.
Bill Inmon’s paradigm:-
Data warehouse is one part of the overall business intelligence system. An enterprise has one data warehouse, and data marts source their information from the data warehouse. In the data warehouse, information is stored in 3rd normal form.
Inmon beliefs in creating a data warehouse on a subject-by-subject area basis. Hence the development of the data warehouse can start with data from the online store. Other subject areas can be added to the data warehouse as their needs arise. Point-of-sale (POS) data can be added later if management decides it is necessary.
Ralph Kimball Methodology-
Kimball views data warehousing as a constituency of data marts. Data marts are focused on delivering business objectives for departments in the organization. And the data warehouse is a conformed dimension of the data marts. Hence a unified view of the enterprise can be obtain from the dimension modeling on a local departmental level.