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Malcolm McRoberts

Online analytical processing - Wikipedia, the free encyclopedia - 0 views

en.wikipedia.org/...Online_analytical_processing

shared by Malcolm McRoberts on 07 Aug 13 - Cached
  • The usual interface to manipulate an OLAP cube is a matrix interface like Pivot tables
  • MOLAP stores this data in an optimized multi-dimensional array storage, rather than in a relational database
  • The problem of deciding which aggregations (views) to calculate is known as the view selection problem. View selection can be constrained by the total size of the selected set of aggregations, the time to update them from changes in the base data, or both. The objective of view selection is typically to minimize the average time to answer OLAP queries, although some studies also minimize the update time
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  • Comparison[edit source | editbeta] Each type has certain benefits, although there is disagreement about the specifics of the benefits between providers. Some MOLAP implementations are prone to database explosion, a phenomenon causing vast amounts of storage space to be used by MOLAP databases when certain common conditions are met: high number of dimensions, pre-calculated results and sparse multidimensional data. MOLAP generally delivers better performance due to specialized indexing and storage optimizations. MOLAP also needs less storage space compared to ROLAP because the specialized storage typically includes compression techniques.[15] ROLAP is generally more scalable.[15] However, large volume pre-processing is difficult to implement efficiently so it is frequently skipped. ROLAP query performance can therefore suffer tremendously. Since ROLAP relies more on the database to perform calculations, it has more limitations in the specialized functions it can use. HOLAP encompasses a range of solutions that attempt to mix the best of ROLAP and MOLAP. It can generally pre-process swiftly, scale well, and offer good function support.
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