Personal Oracle provides a tool called the Navigator, an intuitive graphical tool for managing the objects in a Personal Oracle database as well as remote Oracle databases. You can use the Navigator to define remote connections with which you can manipulate a remote Oracle database, whether it is on a UNIX, NT, or other system.

Other Oracle Products

In addition to the Oracle RDBMS, Oracle Corporation also builds and markets a family of other software products:

• Developer/2000 is a family of tools that support the development of client/server applications. Each of these tools is supported in three different GUI environments: Windows, Mac, and Motif. You will be learning about Developer/2000 in the lessons on Days 12 through 16. Developer/2000 includes:

  Oracle Forms is an enterprise tool for building forms-based applications that are well-integrated with the Oracle database.

  Oracle Reports is a report writer that can tackle the most complex reporting requirements. These reports can be previewed on a screen before being printed.

  Oracle Graphics is a tool for generating presentation graphics from database queries.

  Oracle Procedure Builder is used for the development, maintenance, and testing of software written in a language named PL/SQL, which can be stored and executed from an Oracle database.

PL/SQL is a programming language, developed by Oracle Corporation, that provides procedural extensions to the SQL language. PL/SQL modules exist within an Oracle database to enforce business rules, handle exceptions, and provide functionality that can be invoked from other application development tools.

• Power Objects is another application development environment that is supported in the Windows and Mac environments. The Power Objects user interface is closer to Visual Basic than Oracle Forms. Power Objects also provides object-oriented features such as inheritance.

Inheritance is the mechanism that allows the instances of a class to derive all the properties and methods of the class.

• Designer/2000 is a family of tools that support the development of complex applications that may span many organizations within an enterprise. Each tool supports different roles within the development organization—analyst, database designer, application designer, and programmer. The Designer/2000 components

support the development of logical models, automatic generation of databases, design of business functions, and the generation of application objects such as Oracle Forms applications, Visual Basic programs, and Web applications.

• Database Designer is an entity-relationship diagramming tool that generates an Oracle database from a model. Database Designer is a single-user design tool; it is closely related to one of the components of Designer/2000.
• Precompilers such as Pro*C are software development tools that enable you to embed SQL statements in a program written in a 3GL (third-generation language) such as C, FORTRAN, or COBOL. The appropriate Oracle precompiler translates embedded SQL statements into Oracle library function calls. The translated program can be built as required by the language and operating system.

What Is Client/Server Computing?

In this lesson, you explore both the development of the client/server computing architecture and its future. Most of the application development tools that are discussed in this book support the client/server computing architecture. So, without further delay, let's define what client/server computing architecture is.

Client/server computing architecture consists of one or more computers, designated as the client machines, running an application program which communicates with a remote computer, designated as the server machine, which services requests from the client machines.

In the basic model of client/server architecture, a relational database management system (RDBMS) resides on the server machine. The application program that resides on the client machine interfaces with another software layer, called middleware, that is responsible for communicating requests and their results between the application program and the RDBMS.

The client/server architecture offers several advantages over previous computing architectures:

• It supports a heterogeneous mix of client machines. In today's environment, users may be using Windows 3.11, Windows 95, Windows NT, a Mac, or a UNIX workstation, all of which can be supported by the same server.
• Computing responsibilities are sensibly allocated between client and server. The client machine is responsible for controlling the user interface—displaying information, validating input, and providing meaningful feedback—typically while the server platform is dedicated as a database server.
• It is independent of networking protocol, server platform operating system, and client platform operating system. This independence results in a tremendous amount of flexibility in selecting hardware and software components for a new system or in implementing a client/server application on existing hardware.

With the client/server architecture, the burden of supporting different networking protocols (such as TCP/IP, SPX/IPX, and Named Pipes) and operating systems (such as Windows, Mac, UNIX, and others) rests on the shoulders of various software vendors: the RDBMS vendors such as Oracle, Sybase, Microsoft, and Informix; tool vendors such as Oracle, Powersoft, and Microsoft; and other third-party vendors that supply components such as ODBC drivers for specific platforms and RDBMSs.

The Origins of Client/Server Computing

To appreciate the advantages of the client/server architecture, it is necessary to recall the previous computing architecture. Before the introduction of the PC, a computer system was typically composed of a mainframe computer accessed by many "dumb" terminals. A dumb terminal had no memory of its own and no processing capability; every character displayed on the terminal screen was controlled by a program on the mainframe. This architecture had a number of implications:

• The mainframe computer was responsible for everything: storing and retrieving data, arranging the user interface on all terminals, and validating user input. As the number of active terminals increased, the I/O burden on the mainframe computer also increased. Hardware solutions such as terminal concentrators and multiplexers usually were required to manage the workload.
• The users were completely dependent on the mainframe computer. When the mainframe computer was "down," all computing ceased; a dumb terminal was worthless without the computer to which it was attached. However, in the 1970s, "smart" terminals were introduced which had local memory and limited processing power that could be harnessed by a clever software developer.
• An application program was responsible for "painting" the terminal screen, accepting requests from each user such as a menu pick, validating user input, and managing data storage. With so many responsibilities, a typical application program was quite complex.

Because of the cost of computer hardware and the technical expertise required to make it function, the computer resources of most large organizations were centrally controlled by a single group, usually called the Data Processing (DP) department. Due to the complexity of application programs, there was a significant backlog for developing new applications, typically measured in years. Very quickly, the introduction of the PC changed everything.

The Birth of the PC

In August of 1981, IBM introduced the IBM 5150 PC Personal Computer. Of course, the IBM PC wasn't the world's first personal computer, but there is no question that IBM gave legitimacy to the value of a personal computer. By today's standards, the first PC was quite