Database Reference
In-Depth Information
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Figure 18-14
Sample data allocation scheme.
TRANSPARENCIES
When we introduced DDBMS in an earlier section, we mentioned in passing that a
primary goal for DDBMS is transparency. We will now describe the concept further.
Please note the motivation for transparency and why it must be a primary goal for
DDBMS.
Transparency: Key Ideal
By now, you have realized that a distributed database is a lot more complicated
than a centralized database in design, implementation, architecture, and software
support. By and large, the complexity arises out of the way data are distributed
across various sites. When a user initiates a query or an application executes a
transaction performing database operations, should the user or the application
be concerned about how and where the data are stored, how data will be accessed,
and by exactly what means the results must be consolidated and presented? Not at
all.
The DDBMS must insulate users from these complexities. The DDBMS must
make the data locations and access routes transparent to users. Data access and pro-
cessing must appear to the users as though all data are stored at one site. The overall
ideal goal the DDBMS must strive for is to portray a distributed database to users
as though it is a centralized database.
The DDBMS may provide transparencies at different levels. The actual tech-
niques used by the DDBMS to provide for each level of transparency are quite
intricate. We will not get into all the technical details. Instead, we will broadly
discuss each level of transparency so that you can appreciate its purpose and
significance.
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