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

ROLAP: Relational OLAP

Relational On-Line Analytical Processing (ROLAP) performs dynamic multidimensional analysis of data stored in a relational database, rather than in a multidimensional database. The traditional OLAP's slice and dice functionality is equivalent to adding a WHERE clause in the SQL statement. The design may be structured in the form of a star or its variations. A typical use of ROLAP is for large data size that is infrequently queried, such as historical data.

The chart below highlights advantages and disadvantages of ROLAP.

Advantages Well known environments (relational database).
Can leverage functionality that comes with relational database with ROLAP technologies.
Can be used with data warehouse and OLTP systems.
No pre-aggregation is needed - avoid the data explosion effect that some MOLAP implementations incur with large scale models.
Can handle large amounts of data - the limitation is the data size of the underlying relational database. OLAP itself has no limitation on data amount.
Full security and administration is provided through RDBMSs.
Performs better than MOLAP when the data is sparse.
Performance is getting better by adding more OLAP functions and employing various storage and query optimization techniques.
Disadvantages Performance can be slow, since each ROLAP report is a SQL query in the relational database.
Does not have complex functions that are provided by OLAP tools.
Limited by SQL functionality.
Hard to maintain aggregate tables in the data warehouse.
Major Players

Discover 3 from Oracle, DSS Agent from MicroStrategy, MetaCube from IBM Informix, Platinum Beacon from Platinum, Brio, Business Objects, Cognos Powerplay


ROLAP Architecture
Figure 1. ROLAP architecture