It includes tools for extracting data from multiple operational
databases and external sources; for cleaning, transforming
and integrating this data; for loading data into the data
warehouse; and for periodically refreshing the warehouse to
reflect updates at the sources and to purge data from the
warehouse, perhaps onto slower archival storage. In addition
to the main warehouse, there may be several departmental
data marts. Data in the warehouse and data marts is stored
and managed by one or more warehouse servers, which
present multidimensional views of data to a variety of front
end tools: query tools, report writers, analysis tools, and data
mining tools. Finally, there is a repository for storing and