DW Basics: What is a Data Warehouse ?

So what exactly is a Data Warehouse?. For any BI developer it is very essential to understand the concept of a Data Warehouse. 

Here are the definitions of a Data Warehouse, scrapped from across the internet.

Google - A large store of data accumulated from a wide range of sources within a company and used to guide management decisions.

Oracle - A data warehouse is a relational database that is designed for query and analysis rather than for transaction processing.

Wikipedia - A system used for reporting and data analysis. They store current and historical data and are used for creating analytical reports for knowledge workers throughout the enterprise.

Bill Inmon - A  Data warehouse is a subject-oriented, integrated, time-variant and non-volatile collection of data in support of management's decision making process.

Ralph Kimball - A copy of transaction data specifically structured for query and analysis.

In simple words Data Warehouse is nothing but a database with the following key points, 

• Data analysis and historical data storage is the goal of a Data warehouse.
• Data storage is not a concern and hence all levels of Normalization are not applied here.
• Data from multiple sources are fetched and stored in an organized manner. 
• Data is stored in a structured manner (eg: Star Schema) in order to optimize query and data retrieval process. 
• Basically a high performance server with little constraints on storage and memory usage. 
• Provides fast data throughput.