MOLAP stands for Multidimensional Online Analytical Processing.

MOLAP is an alternative to the ROLAP

ROLAP

ROLAP stands for Relational Online Analytical Processing.ROLAP is an alternative to the MOLAP technology...

 (Relational OLAP

OLAP

In computing, online analytical processing, or OLAP , is an approach to swiftly answer multi-dimensional analytical queries. OLAP is part of the broader category of business intelligence, which also encompasses relational reporting and data mining...

) technology. While both ROLAP and MOLAP analytic tools are designed to allow analysis of data through the use of a multidimensional data model, MOLAP differs significantly in that (in some software) it requires the pre-computation and storage of information in the cube

OLAP cube

An OLAP cube is a data structure that allows fast analysis of data. It can also be defined as the capability of manipulating and analyzing data from multiple perspectives...

 — the operation known as processing. Most MOLAP solutions store this data in an optimized multidimensional array storage, rather than in a relational database

Relational database

A relational database is a database that conforms to relational model theory. The software used in a relational database is called a relational database management system . Colloquial use of the term "relational database" may refer to the RDBMS software, or the relational database itself...

 (i.e. in ROLAP

ROLAP

ROLAP stands for Relational Online Analytical Processing.ROLAP is an alternative to the MOLAP technology...

).

There are many methodologies and algorithms for efficient data storage, aggregation and implementation specific business logic with a MOLAP Solution. As a result there are many misconceptions to what the term specifically implies.

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
  Relational database
  A relational database is a database that conforms to relational model theory. The software used in a relational database is called a relational database management system . Colloquial use of the term "relational database" may refer to the RDBMS software, or the relational database itself...
  
   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 Solutions 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 has changed (usually new data) instead of reprocessing the entire data set.
• MOLAP tools traditionally have difficulty querying models with dimensions with very high cardinality (i.e., millions of members).
• Some MOLAP products have difficulty updating and querying models with more than ten dimensions. This limit differs depending on the complexity and cardinality of the dimensions in question. It also depends on the number of facts or measures stored. Other MOLAP products can handle hundreds of dimensions.
• Some MOLAP methodologies introduce data redundancy.

Trends

Many commercial OLAP

OLAP

In computing, online analytical processing, or OLAP , is an approach to swiftly answer multi-dimensional analytical queries. OLAP is part of the broader category of business intelligence, which also encompasses relational reporting and data mining...

 tools now use a "Hybrid OLAP" (HOLAP

HOLAP

HOLAP is a combination of ROLAP and MOLAP which are other possible implementations of OLAP. HOLAP allows storing part of the data in a MOLAP store and another part of the data in a ROLAP store, allowing a tradeoff of the advantages of each...

) approach, which allows the model designer to decide which portion of the data will be stored in MOLAP .

Products

Examples of commercial products that use MOLAP are Cognos

Cognos

Cognos was an Ottawa, Ontario-based company making business intelligence and performance management software. Founded in 1969, at its peak Cognos employed almost 3,500 people and served more than 23,000 customers in over 135 countries.Originally Quasar Systems Limited, it adopted the Cognos...

 Powerplay, Oracle Database OLAP Option

Oracle OLAP

The Oracle Database OLAP Option implements On-line Analytical Processing within an Oracle database environment. Oracle Corporation markets the Oracle Database OLAP Option as an extra-cost option to supplement the "Enterprise Edition" of its database...

, Microsoft Analysis Services

Microsoft Analysis Services

Microsoft SQL Server Analysis Services is part of Microsoft SQL Server, a database management system. Microsoft has included a number of services in SQL Server related to business intelligence and data warehousing. These services include Integration Services and Analysis Services...

, Essbase

Essbase

Essbase is a multidimensional database management system that provides a multidimensional database platform upon which to build analytic applications. Essbase, whose name derives from "Extended Spread Sheet dataBASE", began as a product of Arbor Software, which merged with Hyperion Software in 1998...

, TM1

Applix

Applix Inc. was a software company founded in 1983 based in Westborough, Massachusetts that published Applix TM1, a MOLAP database server, and related presentation tools, including Applix Web and Applix Executive Viewer. Together, Applix TM1, Applix Web and Applix Executive Viewer were the three...

, Lilith Hicare and Daptech Keystone. There is also an open source MOLAP server Palo

Palo (OLAP database)

Palo is a memory resident multidimensional database server and typically used as a Business Intelligence tool for Controlling and Budgeting purposes with Spreadsheet software acting as the user interface...

.