Databases Reference
In-Depth Information
INTRODUCTION
One of the strengths of PC-based database management systems (DBMSs) is
their flexibility. You can deploy them in various configurations, supporting all
sorts of applications, as part of a small network or to be published on the Inter-
net. This chapter looks at the three most common database configurations for
application support. We start with a look at centralized database configurations
and variations on the traditional client/server model. Then, we'll look at distrib-
uted database configurations that you might use to support enterprise applica-
tions. We finish with a quick look at issues related to supporting Internet-based
applications.
12.1 Supporting a Centralized Database
When PC-based DBMS products were first introduced they were considered an
option for small or specialty database applications. PC hardware capabilities and
the ability of DBMSs to take advantage of that hardware have grown rapidly over
the years to where PC-based DBMSs are usually the first choice when deploying
mission-critical applications.
One important design decision in many database applications is the number
and placement of database servers. Over the years, two basic arrangements for
locating data hosted in database servers have been developed. One, known as a
client/server database, is for personal computers connected together on a local
area network, and is our current focus. This
centralized data environment
is a
configuration based on a single, centralized database. The other, known as a dis-
tributed database, is for larger, geographically dispersed computers located on a
wide area network and using multiple physical databases.
12.1.1 Understanding Local Area Networks (LANs)
A
local area network (LAN)
is an arrangement of personal computers connected
together by communications lines. It is local in the sense that the PCs must be
located fairly close to each other, within a building or within several nearby
buildings. Additional components of the LAN that can be utilized or shared by
the PCs can be other, often more powerful server computers and peripheral
devices such as printers. The PCs on a LAN can certainly operate independently,
but they can also communicate with each other. Finally, a
gateway computer
on the LAN can link the LAN and its PCs to other LANs, to one or more main-
frame computers, or to the Internet.
One of the primary justifications for a LAN is the ability to share resources.
One of the most important resources in any business is information. A key part
of nearly any LAN is one or more file servers that provide central file storage
