Database Reference
In-Depth Information
Clients perform presentation functions
User B
Network
288
Database
Application server
performs business
functions
Database server
runs the DBMS
and performs
database functions
Database
server
Application
server
FIGURE 9-6
Three-tier client/server architecture
NOTE
A client/server system stores the database on a single server, and the DBMS resides and processes on that server. Only with a
DDBMS is the database itself distributed to multiple computers. However, you can combine a DDBMS with a client/server sys-
tem to distribute both data and processing functions across multiple computers.
Advantages of Client/Server Systems
Compared to file server systems, a client/server system has the following advantages:
Lower network traffic. A client/server system transmits only the necessary data, rather than
entire files, across the network.
Improved processing distribution. A client/server system lets you distribute processing func-
tions among multiple computers.
Thinner clients. Because the application and database servers handle most of the processing in
a client/server system, clients do not need to be as powerful or as expensive as they would in a
file-server environment.
Greater processing transparency. As far as a user is concerned, all processing occurs on the
client just as it does on a stand-alone system. Users do not need to learn any special commands
or techniques to work in a client/server environment.
Increased network, hardware, and software transparency. Because client/server systems use
SQL as a common language, it is easier for users to access data from a variety of sources. A sin-
gle operation could access data from different networks, different computers, and different oper-
ating systems.
Improved security. Client/server systems can provide a greater level of security than file server
systems. In addition to the DBMS security features located on the database server, you can place
additional security features on the application servers and on the network.
