Since the introduction of Oracle 8i (not 9i / thanks Kai) it has been possible to define so called "Materialized Views" in the database. The idea is quite simple, namely to pre-generate all the data which a view would return before it is first needed. You can also define indexes and partitioning for the view. It becomes difficult to manage, however, when the underlying data changes frequently.
The following pdf contains all the background information and some examples for getting started.
Salutation