Design, Implementation, and Management of Distributed Databases— An Overview - High-Performance Web Databases: Design, Development, and Deployment - page 350

TODAY'S TECHNOLOGY
In today's distributed database technology, different gateway software
must be used and installed to connect nodes using different distributed
database management system (DBMS) software. Therefore, connectivity
among heterogeneous distributed DBMS nodes is not readily available (i.e.,
available only through selected vendor markets).
In some instances, distributed DBMS software is tied to a single Network
Operating System. This limits the design alternatives for the distributed
DBMS environment to the products of a single vendor. It is advisable to
select a product that supports more than one Network Operating System.
This will increase the possibility of successfully integrating the distributed
DBMS software into existing computer environments.
In reality, distributed databases encompass a wide spectrum of possibil-
ities including:
• remote terminal access to centralized DBMSs (e.g., an airline reserva-
tion system)
• remote terminal access to different DBMSs, but one at a time (e.g.,
Prodigy, COMPUSERVE, and Dow Jones)
• simple pairwise interconnection with data sharing that requires users
to know the data location, data access language, and the log-on proce-
dure to the remote DBMS
• distributed database management with a generic Data Definition Lan-
guage and a Data Manipulation Language at all nodes
• distributed update and transaction management
• distributed databases with replication that support vertical and hori-
zontal fragmentation
•“true” distributed DBMSs with heterogeneous hardware, software, and
communications
The definition of distributed DBMSs lies anywhere along this spectrum.
For the purpose of this chapter, the remote terminal access to data as dis-
cussed in the first two bullets in the preceding list is not considered a dis-
tributed DBMS because a node in the distributed DBMS must have its own
hardware, central processor, and software.
MANAGEMENT MOTIVATION
Some of the problems that currently frustrate managers and technicians
who might otherwise be interested in exploring distributed database solu-
tions include:
• A distributed database environment has all of the problems associated
with the single centralized database environment but at a more
complex level.