Database Reference
In-Depth Information
Internal
sources
Data staging
Metadata
OLAP tools
Reporting
tools
Enterprise
data
warehouse
ETL
process
OLAP
server
Operational
databases
Statistical
tools
External
sources
Data marts
Data mining
tools
Data
sources
Back-end
tier
Data warehouse
tier
OLAP
tier
Front-end
tier
Fig. 3.5
Typical data warehouse architecture
Loading
feeds the data warehouse with the transformed data. This also
includes
refreshing
the data warehouse, that is, propagating updates from
the data sources to the data warehouse at a specified frequency in order
to provide up-to-date data for the decision-making process. Depending on
organizational policies, the refresh frequency may vary from monthly to
several times a day or even near to real time.
ETL processes usually require a data staging area, that is, a database in
which the data extracted from the sources undergoes successive modifications
to eventually be ready to be loaded into the data warehouse. Such a database
is usually called
operational data store
.
3.4.2 Data Warehouse Tier
The data warehouse tier in Fig.
3.5
depicts an enterprise data warehouse
and several data marts. As we have explained, while an
enterprise data
warehouse
is centralized and encompasses an entire organization, a
data
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