In warehousing approach, data from several sources are
extracted, transformed, and loaded into a source called the data
warehouse [1]. With this method, the underlying data sources
are still operational since the data is replicated for the
warehouse. Data warehouses are usually not updated
immediately after a local data source has changed, problems
with this approaches can arise with the freshness of
information. Generally, they are either totally reconstructed,
which is very time consuming, or incrementally updated. Thus,
data warehouses do not contain the most recent data. When an
original information source is updated, but the warehouse still
contains the older information and the ETL [2] process needs to
be executed again. Data warehouses are more effective as longterm
repositories for critical data or as storehouses for historical
data that can be processed and mined. Decision-making support
is one of the important application areas of data warehouses