What is a Data Warehouse(DWH)?

Data Warehouse is a "Subject-Oriented, Integrated, Time-Variant Nonvolatile collection of data in support of decision making".

   In terms of design data warehouse and data mart are almost the same.

In general a Data Warehouse is used on an enterprise level and a Data Marts is used on a business division/department level.  

1.1.                     Subject Oriented

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

1.2.                     Integrated

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

1.3.                     Time-variant

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

1.4.                     Non-volatile

Data is stable in a data warehouse. More data is added but data is never removed.