1. By Timothy Valihora

2.  Information technology specialist and executive
leader Timothy Valihora is the president of TVMG
Consulting. A certified IBM Information Server Expert,
Timothy Valihora provides consulting services to
firms seeking software, system management, and
server solutions.
A data warehouse is a collection of historical data
containing raw material that is used to help analysts
and executives with administration, creating reports,
mining data, and making corporate decisions. When
integrating heterogeneous databases for the
construction of a data warehouse, the two common
approaches include the update-driven approach and
the query-driven approach.

3.  Also referred to as the “lazy integration” approach,
the query-driven approach is used to construct
integrators, known as “mediators,” and wrappers onto
several heterogeneous databases.
Due to the minimal storage requirement, this
approach results in less space and less drainage on
its sources. Additionally, the approach still functions
when the query needs are not known. However, the
query-driven approach requires complex filtering and
integrating processes, and is therefore less efficient
than its counterpart the update-driven approach.
Thus, the query-driven approach often results in
higher costs when frequent queries or aggregations
are involved.