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MOLAP – Multidimensional OLAP

Overview

There are basically three types of online analytical processing: MOLAP, ROLAP, and HOLAP. In this article we’re going to speak about MOLAP particularly. MOLAP is short for multidimensional online analytical processing: it is taken for the traditional version of OLAP. It’s noted for its competitive speed and high user-responsiveness. MOLAP's core attribute constitutes data maintenance in a multidimensional structure which is commonly referred to as a cube. The cube is populated with data from the operational databases (CRM, ERP, AP etc.) or from the data warehouse. The cube includes a fact table in the center and multiple dimensions with the required information. If the cube has more than three dimensions it is taken for a hypercube. Before data processing and analyzing MOLAP tools require precalculating data aggregations to build dimensions for the cube. Due to the aggregations, MDX queries are run rapidly and it’s one of the main MOLAP’s advantages. Nevertheless, the very process of cube build for multidimensional online analytical processing may take up a lot of time depending on the number of aggregations needed to be computed.

Comparison with ROLAP and HOLAP

As compared with MOLAP, ROLAP, as the name implies, operates directly with relational databases. Fact data and dimension tables are stored in relational tables. In contrast to MOLAP tools, ROLAP tools don’t comprise data precomputation and that is the reason why the performance isn’t fast as the queries are composed towards relational tables.

In hybrid OLAP - HOLAP, some aggregations are stored in a multidimensional structure as well as in MOLAP, though sometimes the database exploits relational tables to maintain bigger detailed data quantities. When there’s a need to extract requisite information from HOLAP the system calls the database through information from the fact table, as well as in ROLAP.

Architecture

Benefits

Drawbacks

Products

When it comes to choosing a MOLAP solution out of the range presented in the market it’s good to know such reliable tools as MicroStrategy, Cognos Powerplay, Microsoft Analysis Services, icCube, Oracle Database OLAP Option, TM1, Essbase, etc.

Conclusion