15.4. OLAP MODELS
Have you heard of the terms ROLAP or MOLAP? There is another variation, DOLAP. A very simple explanation of the variations relates to the way data is stored for OLAP. The processing is still online analytical processing, only the storage methodology is different.
ROLAP stands for relational online analytical processing and MOLAP stands for multidimensional online analytical processing. In either case, the information interface is still OLAP. DOLAP stands for desktop online analytical processing. DOLAP is meant to provide portability to users of online analytical processing. In the DOLAP methodology, multidimensional datasets are created and transferred to the desktop machine, requiring only the DOLAP software to exist on that machine. DOLAP is a variation of ROLAP.
15.4.1. Overview of Variations
In the MOLAP model, online analytical processing is best implemented by storing the data multidimensionally, that is, easily viewed in a multidimensional way. Here the data structure is fixed so that the logic to process multidimensional analysis can be based on well-defined methods of establishing data storage coordinates. Usually, multidimensional databases (MDDBs) arc vendors' proprietary systems. On the other hand, the ROLAP model relics on the existing relational DBMS of the data warehouse. OLAP features are provided against the relational database.
See Figure 15-15 contrasting the two models. Notice the MOLAP model shown on the left side of the figure. The OLAP ...
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