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Data Warehouse Explained
Data Warehousing is the main repository of the organisation's historical data, its corporate memory. For example, an organisation would use the information that's stored in its data warehouse to find out what day of the week they had the most transactions in May 2010 or how employee sick leave the week before Christmas differed between Dublin and Galway in 2010.
In other words, the data warehouse contains the raw material for management's decision support system. The critical factor leading to the use of a data warehouse is that a data analyst can perform complex queries and analysis (such as data mining) on the information without slowing down the operational systems.
Data Warehousing Ireland
While operational systems are optimised for simplicity and speed of modification (online transaction processing, or OLTP) through heavy use of database normalisation and an entity-relationship model, the data warehouse is optimized for reporting and analysis (on line analytical processing, or OLAP). Frequently data in data warehouses is heavily denormalised, summarised and/or stored in a dimension-based model but this is not always required to achieve acceptable query response times.
What is a Data Warehouse?
- A Data Warehouse is a set of data structured for Query and Reporting purposes
- Typically contains multiple data sources
- Consolidates data from these sources
- Provides point-in-time reporting
- Can tell you what did or did not happen, or when it happened?
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