A warehouse is a subject-oriented, integrated, time-variant and non-volatile collection of data in support of management's decision making process. Also can define as : the subset of a Business Intelligence tool set responsible for modeling, structuring, storing as well as extraction translation and loading (ETL) of the underlying data needed for analysis.
A copy of transaction data, specially restructured for queries and analyses
A warehouse has the following properties
. Read-only access: Users have read-only access, meaning that the data is primarily loaded into the Data Warehouse via the extraction, transformation and loading (ETL) process.
. Cross-organizational focus: DataSources from the entire organization (production, sales and distribution, controlling), and possibly external sources, make up the basis of the system.
. Data Warehouse data is stored persistently over a particular time period.
. Data is stored on a long-term basis.
. Designed for efficient query processing: The technical environment and data structures are optimized to answer business questions . not to quickly store transactions.