From http://www.reportportal.com/xmla.asp :

What is OLAP?

OLAP (On-Line Analytical Processing) is a technology that provides solution to three fundamental reporting problems:

1. Slowly running reports. For example, calculating total sales for all products might take very long time. Moreover, each report might keep calculating the same value all over again. To resolve this problem, OLAP can store all possible totals in summary (aggregation) tables. The aggregations are usually re-calculated daily or hourly.

2. Report Explosion. The number of possible static reports that can be created from a database may be too large. For example, we have a sales table with three columns: product, date and dollars. Suppose that we sell just 10 products and we have just 10 days worth of data. We can have 29 possible reports:
Total sales
Total sales by product
Total sales by product for each day - 10 reports
Total sales by date
Total sales by date for each product - 10 reports
Total sales by date (rows) and product (columns)
Total sales by date (columns) and product (rows)
Total sales by date (rows) and product (rows)
Total sales by product (rows) and date (rows)
Total sales by date (columns) and product (columns)
Total sales by product (columns) and date (columns)

If we are to add an additional column: "customer name" to our table, the number of possible reports would increase exponentially. Because an average organization can have much more than three columns associated with its sales, the number of possible reports can approach or exceed trillions!

OLAP technology allows users to design and modify reports themselves via a simple drag and drop interface, eliminating the need of having an "army" of report writers on staff.

3. Statistical calculations are usually not supported by a relational database. For example, SQL (Structured Query Language) requires users to run multiple queries to get the mean, median or the standard deviation. Because OLAP has pre-calculates totals, it supports a wide range of statistical functionality that can be calculated in a single step.

Last edited Dec 24, 2012 at 1:52 AM by grand, version 2

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