Database Reference
In-Depth Information
Section 2.7 of Chapter 2 mentioned some connectivity possibilities. Here are a few
noteworthy points to remember:
1.
From the definition, the user is given the notion of virtual
database systems consisting of data that may reside anywhere
in the network.
2.
The sites may be distributed over a wide geographical area,
or in a local area/building. A distributed database system can
therefore be a LAN (local area network), a MAN (metropolitan
area network), or a WAN (wide area network).
3.
Distributed database systems are not to be confused with
remote access systems, sometimes called distributive
processing systems. The latter has been around for some
time. In such systems, the user accesses data at remote sites
but the operation is not seamless; the user is aware and the
consequences may be obvious. In a distributed database
system, access across sites is seamless.
The literature [on electronic communications and computer networks] documents
several alternate approaches to setting up a distributed database. Three prevalent ones
are as follows:
•
Using client-server technology to set up a federated database
•
Setting up a virtual private network (VPN)
•
Setting up a data warehouse
There is no shortage of information on client-server technology and VPNs.
Exploration of this is beyond the scope of this course; however, references [Martin, 1995]
and [Ozsu, 1999] should provide you with a useful start. Suffice it to say that Oracle
as described earlier (Chapters 10-16) qualifies as a distributed DBMS. When you
install Oracle Server on a node in a network, that node acts as a database server. If you
then install Oracle Client on other nodes in the network, your database server can be
accessed from anywhere in the network (as well as from other network systems with Web
accessibility) in a seamless manner. Also, Chapters 24 and 25 provide overview of data
warehousing and Web-accessible databases respectively.
22.2 Advantages of Distributed Database
Systems
Figure
22-1
provides some benefits that distributed database systems provide.
The benefits may be summarized in three categories:
•
Efficiency and Productivity
•
Convenience
•
Reliability
