Sql server - Explain the storage models of OLAP

Explain the storage models of OLAP.

MOLAP Multidimensional Online Analytical processing
In MOLAP data is stored in form of multidimensional cubes and not in relational databases.

- Excellent query performance as the cubes have all calculations pre-generated during creation of the cube.

- It can handle only a limited amount of data. Since all calculations have been pre-generated, the cube cannot be created from a large amount of data.

- It requires huge investment as cube technology is proprietary and the knowledge base may not exist in the organization.

ROLAP Relational Online Analytical processing
The data is stored in relational databases.

- It can handle a large amount of data and
- It provides all the functionalities of the relational database.

- It is slow.
- The limitations of the SQL apply to the ROLAP too.

HOLAP Hybrid Online Analytical processing
HOLAP is a combination of the above two models. It combines the advantages in the following manner:

For summarized information it makes use of the cube.
For drill down operations, it uses ROLAP.

Explain the storage models of OLAP.

There are three storage models in OLAP:

--Relational Online Analytical processing model
--Multidimensional Online Analytical Processing model
--Hybrid Online Analytical Processing model.

Relational Online Analytical processing model:

The data is stored in relational databases and provides an appearance of traditional OLAP’s slicing and dicing functionality. The advantage of using ROLAP is large amount of data can be handled and leverage the relational database functionalities.

Multidimensional Online Analytical processing model:

A traditional mode in OLAP analysis. Data in this model is stored in the form of multidimensional cubes. The advantage is that it provides an excellent query performance and building cubes for fast data retrieval. The calculations are pre-generated at the time of creating cube and easily applied while querying data.

Hybrid Online Analytical processing model.

HOLAP combines the strengths of both ROLAP and MOLAP. HOLAP leverages the cube technology and ROLAP model is used for drilling down into details.
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