The explosion in the use of the World Wide Web and Web browsers led RDBMS vendors, such as Oracle, to develop tools that would support the dynamic display of database content on the Web. Simultaneously, the Java language—platform-independent, object-oriented, distributed, and secure—appealed to software vendors, long interested in writing software once and deploying it on a variety of computer hardware and operating system platforms. With these two movements, many software vendors began advocating the "thin" client model: a user interface, based on a Web browser in which a Java applet is downloaded by a server to be executed on the client machine. The traditional client/server architecture was referred to as the "fat" client model because the client required a typically large executable for the application program (for example, mybigapp.exe), multiple libraries (such as DLLs), as well as the middleware drivers (such as SQL*Net).

The arguments in support of the thin client model are

• It significantly reduces the administrative costs for client machines.
• Applications are written once and can be deployed everywhere.
• Updates to applications are made on one machine: the server.
• Portability: Instead of being tied to a particular client machine, an application "follows" the authorized user.

However, there are concerns about the viability of the thin client model:

• Because all application software is downloaded from a server, the thin client model increases the load on the network.
• Because Java is a byte-code interpreted language, it is not as fast as other languages; performance may be an issue.

CORBA

In 1989, the Object Management Group (OMG) was established by representatives from hardware manufacturers, software vendors, researchers, and software practitioners. The OMG's goal was to promote the use of object-based software. To this end, the OMG developed a conceptual foundation called the Object Management Architecture. From this foundation, a specification was developed for the Common Object Request Broker Architecture, commonly referred to as CORBA.

The CORBA specification describes several components:

• An Object Request Broker (ORB) that supports requests and responses between objects in a heterogeneous, distributed environment.
• Object Services, which is a set of basic services that support the use and implementation of objects.
• Common Facilities, which is a set of services that applications may share.
• Application Objects, which are vendor- or developer-supplied objects with a defined interface.

In support of the CORBA 2.0 specification, Oracle has unveiled an architecture named the Network Computing Architecture (NCA). Oracle's latest version of Oracle WebServer, version 3.0, is aligned with the vision of the Network Computing Architecture. You'll be learning more about NCA in Day 21, "Oracle: The Next Generation."

The Challenge to Client/Server
Computing: The Network Computer

For some time, Oracle CEO Larry Ellison has complained that PCs are too expensive and complex for the average user. His vision is a device called a network computer that would cost less than the typical PC and be far simpler to administer because all of its software would be downloaded via a Web browser.

In 1996, Oracle Corporation established a subsidiary company, Network Computer, Incorporated. The mission of this subsidiary is to license its network computer design to hardware manufacturers and promote the development of applications for the device.

The Purpose of This Book

This book is designed to serve readers who fit into the following categories:

• You are familiar with databases such as dBASE or FoxPro but haven't worked with Oracle or other SQL-based database products.
• You have some experience with SQL but want to learn more about its use in an Oracle database.
• You are familiar with 3GLs such as COBOL but you don't have experience in the client/server environment and want to learn about application development environments such as Developer/2000 or Power Objects.
  To illustrate the concepts presented in the book, you will see many examples based on the design of a database for a small college. The examples based on this database are augmented with other specific examples, depending on the topic under discussion. The

CD-ROM contains this sample database as well as relevant files from each of the chapters in the book. Refer to the Introduction of this book for more information about the CD-ROM.

When you have finished reading this book, you'll be familiar with the following languages, tools, and issues:

• SQL: the de facto industry and ANSI standard language for interacting with relational databases. You'll learn more about SQL on Days 4 through 8.
• PL/SQL: Oracle's procedural language extensions to SQL, used for writing database triggers and stored procedures and functions. Days 9 through 11 provide a solid introduction to PL/SQL.

• Developer/2000: You should be able to develop a basic Oracle Forms application, build a master-detail report with Oracle Reports, and use Procedure Builder to modify a database trigger or package. You'll spend five lessons, Days 12 through 16, learning about Developer/2000.
• Power Objects: You will be able to develop a Power Objects application with data entry, query, and reporting capabilities; you'll spend two lessons, Days 17 and 18, on the use of Power Objects.

To get the most from this book, at a minimum you should have an Oracle database available to you—either Personal Oracle7, an Oracle Workgroup Server, or an Oracle Universal Server—and SQL*Plus. However, you'll probably need to have Developer/2000 and Power Objects to follow the lessons dealing with these tools.

Summary

The crucial ideas about client/server computing introduced in this lesson are as follows:

• The theoretical foundation for relational databases began in 1970.
• Structured Query Language (SQL) is an official standard language for communicating with a relational database.
• There are three configurations of the Oracle Relational Database Management System (RDBMS): the Oracle Universal Server, the Oracle Workgroup Server, and Personal Oracle.
• The client/server architecture supports a variety of client platforms, server platforms, and networking protocols.
• The client/server architecture requires the use of a software layer called middleware, whose function is to support protocol-independent communication between the client machine and the server machine.
• A two-tier architecture consists of a client machine communicating directly with a database server.
• A three-tier architecture consists of a client machine communicating with an appli-cation server. The application server, in turn, communicates with the database server.
• The popularity of the World Wide Web and the Java programming language are piquing the interest of many software developers in a thin client model: a Web browser which downloads Java applets, as required.

What Comes Next?

On Day 2, "Guidelines for Developing an Oracle Application," you learn about some of the basic steps that are required to build an Oracle application, such as gathering user requirements.