Model database in implementation level


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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