Online Analytical Processing (OLAP) and Business

There are many business intelligence tools available to help make sense of the huge volumes of data that the average business must process. One of the most commonly used methods is Online Analytical Processing, also known as OLAP.
OLAP is only one kind of data analysis method but it is particularly useful in certain business circumstances such as process management, forecasting, budgeting, marketing and financial reporting among other areas. One of its defining features is that the databases allow complex queries that return results quickly.
OLAP systems run on the OLAP cube concept and have the potential to return results from queries in a fraction of the time taken by other methods. There are a number of different types of OLAP system.
    Multidimensional - MOLAP
    This is also simply known as OLAP and uses databases whose structures are optimized in advance for certain functionalities. Advantages include the fact that query results are returned very quickly and data can be stored using much smaller space than relational databases.
    Relational - ROLAP
    ROLAP differs from MOLAP in that it does not require any pre-computation, nor does it need to store any information. All information is accessed directly from the relational database. It can use standard query language (SQL) queries to request certain information from the database and present it to the end user. One of the main advantages of ROLAP is that it can handle very large volumes of data. Also, because data is stored on a standard relational database it can be accessed by SQL queries and presented with normal reporting tools.
    Hybrid - HOLAP
    There is no exact consensus on what a HOLAP is precisely, but as you might imagine it combines features of both multidimensional and relational OLAPs. In this scenario, some of the data will be kept in the MOLAP store and the rest in the ROLAP store. It is up to the designer how much and what kind of data is kept in each, and how it is partitioned.
    These are the three main types of OLAPs you will encounter. However, you may also hear of the following:
          o WOLAP - Web-based OLAP
          o DOLAP - Desktop OLAP
          o RTOLAP - Real-Time OLAP
          o SOLAP - Spatial OLAP
    There are a range of OLAP products on the market today, however the most commonly used by far is Microsoft Analysis Services, which has been available since 1998. There are also a number of other commercial offerings like Hyperion and Cognos. Since 2000, a number of open source products have emerged including Palo and Mondrian.

SOURCE:http://www.relativitycorp.com/data/article1.html