Oracle Tips  by Burleson Consulting

The Data Warehouse Development Life Cycle

Online Analytical Processing and Oracle
OLAP Fundamentals

Essentially, an OLAP system is any system that captures summarized information and allows the summaries to be displayed as cross-tabulations between two variables. In the following example, we explore OLAP using the Excel spreadsheet pivot table feature.

The terms OLAP and multidimensional database have become synonymous, thus adding to the confusion surrounding the two terms. Essentially, a multidimensional database is a database architecture that stores summarized information such that all salient data items (called dimensions) are cross-referenced with each other (see Figure 5.1). For example, a multidimensional database might store sales totals cross-referenced by month, product line, territory, and salesperson. The multidimensional database could then display the sales totals according to the possible combinations of cross-referenced tables shown in Table 5.1.

Fact                                  Dimensions
Total Sales                   Month by product line
Total Sales                   Month by territory
Total Sales                   Month by salesperson
Total Sales                   Product line by territory
Total Sales                   Product line by salesperson

Table 5.1 Possible plots of facts and dimensions.

Figure 5.1 A sample OLAP display.

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This is an excerpt from "High Performance Data Warehousing". To learn more about Oracle, try "Oracle Tuning: The Definitive Reference", by Donald K. Burleson.  You can buy it direct from the publisher at 30% off here:
http://www.rampant-books.com/book_1002_oracle_tuning_definitive_reference_2nd_ed.htm