Database Warehouse
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OLAP
OLAP, On-Line Analytical Processing, can be defined as a Fast Analysis of Shared Multidimensional Information or FASMI for short.
OLAP is considered to be fast because it is able to deliver responses in about five seconds, with the simplest analysis taking no more than one second and very few taking more than 20 seconds.
A research was done in the Netherlands and showed that end-users assume that a process has failed if results are not received in 30 seconds and they are apt to hit 'ctrl-alt-del' unless the systems notifies them that a report will take longer. Even when the users are notified that the report will take longer, they are likely to get distracted and lose their train of thought, so the quality of analysis suffers.
It is hard to achieve high speed if there are large amounts of data, particularly if on-the-fly and ad hoc calculations are required. A wide variety of techniques are used to achieve this goal utilizing specialized forms of data, extensive pre-calculations, and specific hardware requirements. Even with these upgrades, there is not a product fully optimized, therefore it is expected that this will be an area of developing technology. The full pre-calculation approach fails with very large, sparse applications as the databases get too large, whereas doing everything on-the-fly is much too slow with large databases, even when sophisticated hardware is used. Although it seemed miraculous at first if reports that previously took days now only takes minutes, users soon get bored of waiting and the projects will be much less successful than if it had delivered a near instantaneous response, even at the last of less detailed analysis.
A survey taken of OLAP users found that slower query response is consistently the most often cited technical problem with OLAP products...