Data warehouses are designed in such a way that they are optimised for speed of data retrieval. To assist in speeding data retrieval, the data stored in the data warehouse is often stored multiple times, both in their most granular and summarized (aggregated) forms.
It is possible to set up a data warehouse so the simpler queries and reports can be written with little technical knowledge. But usually it is advisable to use members of the IT department write and maintain queries and reports written against data warehouse data. This will speed up the set up process and avoid any future problems.
It is common practice to purge the older data from transaction processing systems to enable the response time to be kept under control. For the purpose of querying and reporting, both the purged and current data can be stored in the data warehouse where there is usually a lower requirement to control response times or the response times are at a higher level.
A major concern within data warehousing, query and reporting is security, particularly to those to firms that want to allow report and querying only over the Internet. They need to limit the access to those who only need to query and report transaction processing system data so they have no visibility to the transaction processing system databases.
Data warehousing, as with any other technological niche, has a history of innovations that are not accepted by the market for whatever reason. These reasons are normally related to implementation costs or that the market is just not aware of the advantages that they can give.
About the Author: Mike has more than 15 years ox experience designing and implementing Data warehouses based on Oracle, MS SQL Server, MySql, PostgreSQL and more he is currently working for DB Software Laboratory