Data Warehousing

Data Warehouse:

The term Data Warehouse was coined by Bill Inmon in 1990, which he defined in the following way: "A warehouse is a subject-oriented, integrated, time-variant and non-volatile collection of data in support of management's decision making process". He defined the terms in the sentence as follows:

Subject Oriented:

Data that gives information about a particular subject instead of about a company's ongoing operations.

Integrated:

Data that is gathered into the data warehouse from a variety of sources and merged into a coherent whole.

Time-variant:

All data in the data warehouse is identified with a particular time period.

Non-volatile

Data is stable in a data warehouse. More data is added but data is never removed. This enables management to gain a consistent picture of the business.

 

There are three types of data warehouses:

1.Enterprise Data Warehouse - An enterprise data warehouse provides a central database for decision support throughout the enterprise.

2.ODS(Operational Data Store) - This has a broad enterprise wide scope, but unlike the real entertprise data warehouse, data is refreshed in near real time and used for routine business activity. One of the typical applications of the ODS (Operational Data Store) is to hold the recent data before migration to the Data Warehouse.Typically, the ODS are not conceptually equivalent to the Data Warehouse albeit do store the data that have a deeper level of the history than that of the OLTP data.

3.Data Mart - Datamart is a subset of data warehouse and it supports a particular region, business unit or business function.