Link: http://www.oracle-developer.net/display.php?id=510

"Oracle has supported stored expressions for many years, in views and function-based indexes. Most commonly, views enable us to store and modularise computations and expressions based on their underlying tables' columns. In more recent versions (since around the 8i timeframe), we have been able to index expressions using function-based indexes. Now, with the release of 11g, Oracle enables us to store expressions directly in the base tables themselves as virtual columns.

As we will see in this article, virtual columns are more flexible than any of their prior alternatives. We will examine their basic usage and also consider some of the performance aspects of the new feature."