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Another development in the database area that was the result of the proliferation of
computer networks was that of distributed database systems. A distributed
database system seamlessly integrates multiple databases located on different
computers. These computers may be located in the same building or may be
geographically far apart (such as in different cities). Note that unlike a clientserver database system in which there is only one database, a distributed database
system has multiple databases integrated together to serve as a single database.
The main motivation behind using a distributed database system is to store data in
the most convenient places within a computer network, depending on data entry
requirements, storage capacity availability, processing load requirements, data
security requirements, and so on. For example, as shown in Figure 16.21, a
distributed database system might integrate employee databases of different
departments of an organization that are located in different cities. Each
department's database stores the records of the employees working in that
A distributed database management system functions in such a manner that the
multiple distributed databases managed by it appear as a single centralized
database to the end users. That is. a user making a request would not be concerned
about the source of the data or how they are retrieved. For example, in the
distributed database system of Figure 16.21, a user can simply make a single
request for a sorted list of all female employees in the organization who are more
than 40 years old. The distributed database management system takes care of
sending this request to all the four databases, then accumulating the results, sorting
it, and presenting it to the user. All this is done internally without the knowledge
of the user making the request.
Active Database Systems
Traditional database management systems are passive in the sense that commands
are executed by the database (such as, query, update, delete) as and when
requested by the u...
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This document was uploaded on 04/07/2014.
- Spring '14