Web-enabled OLAP Tutorial

- DW Overview

--------Back-end Tools

- Intro to OLAP

--------Codd's 12 Rules

- MD Data Structures

- OLAP Server

- OLAP Operations

- OLAP Architectures

--------MOLAP: Part I
--------MOLAP: Part II
--------ROLAP: Part I
--------ROLAP: Part II

- Data Explosion

- OLAP Criteria

- Glossary

- References

MOLAP: Multidimensional OLAP

As explained in the previous section, MOLAP utilizes a proprietary multidimensional database to provide OLAP analyses. The main premise of this architecture is that data must be stored multidimensionally to be viewed multidimensionally.

Data from various operational systems is loaded into a multidimensional database through a series of batch routines. Once this atomic data has been loaded into the multidimensional database, the general approach is to perform a series of calculations in batch to aggregate along the dimensions and fill the multidimensional array structures. Then indices are created, and hashing algorithms are used to improve query access time.

When users request OLAP reports through the interface, the application logic layer of the multidimensional database retrieves the stored data. It reads the pre-compiled data and has limited capabilities to dynamically create aggregations or to calculate metrics that have not been pre-calculated and stored.

MOLAP is a two-tier, client/server architecture. The multidimensional database serves as both the database layer and the application logic layer. In the database layer, it is responsible for all data storage, access, and retrieval processes. In the application logic layer, it is responsible for the execution of all OLAP requests. The presentation layer integrates with the application logic layer and provides an interface through which the users view and request OLAP analyses. The client/server architecture allows multiple users to access the same multidimensional database.

MOLAP Architecture
Figure 1. MOLAP architecture