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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