During this time of rapid change and advancement, a new type of system
appeared. Called client/server development because processing is split
between client computers and a database server, this new breed of
application was a radical change from mainframe-based application
programming. Among the many advantages of this type of architecture are
• Reduced maintenance costs
• Reduced network load processing occurs on database server or client
computer
• Multiple operating systems that can interoperate as long as they share
a common network protocol
• Improved data integrity owing to centralized data location
Oracle Corporation released the first commercial RDBMS that used SQL.
Although the original versions were developed for VAX/VMS systems,
Oracle was one of the first vendors to release a DOS version of its
RDBMS. (Oracle is now available on more than 70 platforms.) In the
mid-1980s Sybase released its RDBMS, SQL Server. With client libraries
for database access, support for stored procedures (discussed on Day 14,
"Dynamic Uses of SQL"), and interoperability with various networks, SQL
Server became a successful product, particularly in client/server
environments. One of the strongest points for both of these SQL Server
powerful database systems is their scalability across platforms. C
language code (combined with SQL) written for Oracle on a PC is
virtually identical to its counterpart written for an Oracle database
running on a VAX system. SQL is the de facto standard language used to
manipulate and retrieve data from these relational databases. SQL
enables a programmer or database administrator to do the following:
• Modify a database's structure
• Change system security settings
• Add user permissions on databases or tables
• Query a database for information
• Update the contents of a database
In putting into practice Client/Server figure, Bernard H. Boar
classifies client/server computing as follows:
Client/server computing is a processing model in which a single
application is partitioned between multiple processors (front-end and
back-end) and the processors cooperate (transparent to the end user) to
complete the processing as a single unified task. Implementing
Client/Server Computing A client/server bond product ties the processors
together to provide a single system image (illusion). Shareable
resources are positioned as requestor clients that access authorized
services. The architecture is endlessly recursive; in turn, servers can
become clients and request services of other servers on the network, and
so on and so on. This type of application development requires an
entirely new set of programming skills. User interface programming is
now written for graphical user interfaces, whether it be MS Windows, IBM
OS/2, Apple Macintosh, or the UNIX X-Window system. Using SQL and a
network connection, the application can interface to a database residing
on a remote server. The increased power of personal computer hardware
enables critical database information to be stored on a relatively
inexpensive standalone server. In addition, this server can be replaced
later with little or no change to the client applications.
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