Editing Online analytical processing (section)

===Multidimensional OLAP (MOLAP)===
MOLAP (multi-dimensional online analytical processing) is the classic form of OLAP and is sometimes referred to as just OLAP. MOLAP stores this data in an optimized multi-dimensional array storage, rather than in a relational database.

Some MOLAP tools require the [[pre-computation]] and storage of derived data, such as consolidations – the operation known as processing. Such MOLAP tools generally utilize a pre-calculated data set referred to as a [[data cube]]. The data cube contains all the possible answers to a given range of questions. As a result, they have a very fast response to queries. On the other hand, updating can take a long time depending on the degree of pre-computation. Pre-computation can also lead to what is known as data explosion.

Other MOLAP tools, particularly those that implement the [[Functional Database Model|functional database model]] do not pre-compute derived data but make all calculations on demand other than those that were previously requested and stored in a cache.

'''Advantages of MOLAP'''
* Fast query performance due to optimized storage, multidimensional indexing and caching.
* Smaller on-disk size of data compared to data stored in [[relational database]] due to compression techniques.
* Automated computation of higher-level aggregates of the data.
* It is very compact for low dimension data sets.
* Array models provide natural indexing.
* Effective data extraction achieved through the pre-structuring of aggregated data.

'''Disadvantages of MOLAP'''
* Within some MOLAP systems the processing step (data load) can be quite lengthy, especially on large data volumes. This is usually remedied by doing only incremental processing, i.e., processing only the data which have changed (usually new data) instead of reprocessing the entire data set.
* Some MOLAP methodologies introduce data redundancy.

====Products====
Examples of commercial products that use MOLAP are [[Cognos]] Powerplay, [[Oracle OLAP|Oracle Database OLAP Option]], [[MicroStrategy]], [[Microsoft Analysis Services]], [[Essbase]], [[Applix|TM1]], [[Jedox]], and icCube.