DISTRIBUTED DATABASE SYSTEMS - Database Design and Development: An Essential Guide for IT Professionals - page 547

DDBMS—its functions and features. Later, we will consider all aspects of process-
ing queries and transactions in a distributed database environment. But, before
covering all of these, first let us summarize the advantages and disadvantages, and
then move on.

Advantages Here is the list of major advantages:

Suitable structure. A modern enterprise has users in dispersed locations who need
to access primarily local data and, less frequently, global data. Now note the struc-
ture of a distributed database with data spread across dispersed locations and yet
any data available from anywhere. This structure is well suited for many of today's
corporations.

Desirable local autonomy. Users at each site can have autonomy in owning and
controlling their local data.

Preserved shareability. Data sharing, a principal motivation for database systems,
is still available in a distributed database. All data in the distributed database may
be shared by users at all sites.

Improved availability. If the computer system where a centralized database resides
goes down, all the data become unavailable to users. However, in a distributed
environment, only the part of the data that resides in the failed site becomes
unavailable.

Enhanced reliability. Reliability ensures continuous operation of a database system.
Even when one site is down, other sites can continue operation, and, in special
circumstances, other sites may pick up the operations of the failed site until it is
restored.

Better efficiency. As you know, users at each site demand local data much more
than global data. Local data may be accessed quite efficiently.

Reduced transmission costs. For global enterprises, compared to centralized data-
bases, distributed databases incur lower data communication costs.

Easier growth. A distributed database provides for modular growth. When a new
office is opened at a remote location, simply add a new site or node in your distri-
bution network.

Disadvantages Note the following potential disadvantages presented by distrib-
uted database systems. However, it is expected that, as distributed database prod-
ucts mature and become more robust, some of the disadvantages are likely to be
less troublesome.

Increased complexity. Making the nature of distribution transparent to users, frag-
menting and replicating of data, routing of queries and transactions—all these and
other similar issues add to the complexity of distributed database systems.