Oracle9iR2 Data Warehousing
This book will show you how to use the Oracle database with tools such as Oracle Discoverer to query the warehouse, generate reports that can be deployed over the web, and gain better insight into your business.
TABLE OF CONTENTS Oracle9iR2 Data Warehousing
Chapter 9: Oracle 9i OLAP and Data Mining
No book on data warehousing would be complete without a discussion of its two important applications OLAP and data mining. In Oracle 9 i, OLAP and Data Mining functionality are now integrated into the database server and are available as options to the Enterprise Edition of the database. We will discuss each of these options in this chapter.
9.1 Oracle OLAP
Online Analytical Processing (OLAP) is used to answer queries that provide information about your business. OLAP queries typically perform complex calculations, such as period-over-period comparisons, finding top-N products, time series analyses, and sales forecasting. The data is analyzed along multiple dimensions, such as product, geography, and time. Hence, this type of data is often called multidimensional data.
ROLAP versus MOLAP
Ever since the OLAP industry started, there has been an ongoing debate about the best way to store multidimensional data. One school of thought advocated storing data in tables in relational databases, which are known for their ability to scale to large amounts of data. This is known as Relational OLAP (ROLAP). In this case, analysis of data is done using SQL queries all of the SQL features discussed in this book would be useful for relational OLAP. The other school of thought felt that multidimensional data processing should be done using a specialized storage format (called a multidimensional database or MDDB) designed to quickly answer OLAP queries. This is known as Multidimensional OLAP (MOLAP). Many vendors provide MOLAP capabilities, including Oracle's own Express Server product. The...
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