Databases Reference
In-Depth Information
SELF-CHECK
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Can a traditional centralized data environment have multiple data-
base servers as long as they are all deployed on the same LAN?
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What does a three-tier data environment include?
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What is a data warehouse used to support?
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What is a multi-purposed server?
12.2 Supporting a Distributed Database
In today's world of universal dependence on information systems, all sorts of
people need access to a company's databases. These people include a company's
own employees, its customers, potential customers, suppliers, and vendors of all
types. It is possible for a company to have all of its databases concentrated at
one mainframe computer site with worldwide access provided by telecommuni-
cations networks. However, even though a centralized system like this can be
advantageous, it poses some problems as well. For example, if the single site
goes down, then everyone is blocked from accessing the company's database.
Also the communications costs from the many far-flung PCs and terminals to
the central site can be prohibitive.
As an example, we're going to use a large multinational company with major
sites in Los Angeles, Memphis, New York (corporate headquarters), Paris, and
Tokyo. Let's say that the company has a transactional relational database that is
actively used by all five sites. There are six tables, named A, B, C, D, E, and F,
and response time regarding queries made to the databases is an important fac-
tor. Figure 12-3 shows a centralized configuration with all of the tables hosted
on the database physically located in New York.
While we are discussing distributed databases and related support issues, we'll
use this example to see options available to distribute and maintain the data.
12.2.1 Understanding Distributed Data
The reasons for implementing distributed data environments can vary as much
as the companies using those environments to meet their data requirements. The
reasons and justifications for using a distributed data environment, however, usu-
ally come down to one or more of the following (in no particular order):
Reduce costs.
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Make the data universally available.
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