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Unformatted text preview: t of every data warehouse is the metadata. Simply stated,
metadata is data about data. It is a catalog of information that keeps track of what
is where, in the data warehouse. The metadata of a data warehouse typically
stores the definitions of source data, target data, source to target mappings,
transformation information, and update information. It is an integral part of a data
warehouse, which must be constructed along with the data warehouse.
Metadata is to a data warehouse what road map is to a navigator. It is the key to
providing users and developers with a road map to the information in the data
Drill Down and Roll Up Analyses
Information from a data warehouse can be extracted and viewed as per the
requirement of the end user. Both aggregated as well as detailed information can
be arrived at, depending on the analysis being carried out on the data. The process
of viewing information from a higher level (in the hierarchy) to a more detailed
view of information is known as drilling down on the data. Conversely, viewing
information from the detailed level up to a higher level is known as rolling up on
For example, suppose there is a data warehouse containing citizen data for the
whole country. Now a query analysis to find out the percentage of people areawise in different occupations can be carried out at city/village level, district level
(each district comprising of several cities and villages), state level (each state
comprising o several districts), and country level (the country comprising of
several states). A user may carry out drill down analysis by starting the analysis at
state level and gradually extracting this information for individual districts and
cities/villages of interest. On the other hand, a user may carry out roll up analysis
by starting the analysis at city/village level and gradually extracting aggregated
information for districts, states, and the country.
ROLAP and MOLAP
We saw that OLAP systems are designed to support effective decision-making.
The two popular architectures for O...
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This document was uploaded on 04/07/2014.
- Spring '14