There are also some disadvantages to coding your Web application in PL/SQL:

• Unlike a Java applet, a PL/SQL subprogram that dynamically generates HTML tags is limited to the user interface available in HTML. In other words, a user's input will not be validated until the user submits the form by pressing a button.
• PL/SQL does not offer the object-oriented features that exist in languages like Java. Even with the object-relational features introduced in the Oracle8 server and PL/SQL 3.0, this remains true.
• Except for Designer/2000, there are no development environments that will allow you to graphically construct a Web form and generate the PL/SQL code to implement it. And Designer/2000, version 1.3, is limited to the generation of Web forms that only query an Oracle database.

Developing Web Applications with Java

There are several Java development environments, such as Symantec Café, that can be used to develop a Java applet which can be invoked from a Web browser. These products typically use a JDBC driver—similar to an ODBC driver—to access a relational database. There are some advantages to this development approach:

• You have control over the look and feel of the applet user interface.
• By including field-level validation, the applet user interface can be less frustrating for the user. The applet can prevent the user from navigating to the next field if the current field contains an invalid value.
• The applet can support a heterogeneous environment. With a JDBC driver, the applet can simultaneously connect to different vendor databases and present a cohesive view of related information.

Let's ponder the negative aspects of this development approach:

• By using a JDBC driver, the applet is not as well integrated with the Oracle database as Developer/2000 for the Web or PL/SQL. You may not be able to use as many features as are available through the Oracle-supplied tools.
• Because you have responsibility for the user interface, you have to write a considerable amount of Java code.

Developing Web Applications with Other Software
Packages

There are several software packages, such as Cold Fusion and Tango, that provide a graphical interface for developing a Web application. Generally, these products require the installation of an application server on either a Sun Solaris or Windows NT server. The application server accesses an Oracle database via an ODBC driver. There are some clear advantages to these packages:

• They are quite easy to use. An inexperienced developer can build an application in a matter of days.
• Because the generated HTML code includes calls to the application server, the resulting applications can include field-level validation.

There are also some aspects of these tools that you should be aware of:

• Because these packages typically use an ODBC driver to access an Oracle database, you may not be able to use many features available in the Oracle server.
• Depending on the product that you choose, the resulting Web application may not prevent two users from modifying the same record at the same time. If you are building a query-only application, this isn't a concern. However, if you are building a Web application that will allow a user to add, modify, or delete database records, you need to investigate the support that the software package provides for record locking.

Oracle's Network Computing Architecture

In September 1996, Oracle Corporation introduced a strategy for future software development: the Network Computing Architecture (NCA). The key factors that influenced the creation of the NCA are as follows:

• Explosive growth of the Internet and the World Wide Web
• Increasing complexity and expense to administer client/server applications on a variety of client platforms such as PCs, Macs, and UNIX workstations
• Support for objects
• Support for multiple programming languages
• Support for distributed application and database servers
• Continued support for legacy applications (for example, client/server)

Overview of the Network Computing Architecture

It is important to understand that the NCA is a strategy for commercial software development that will be implemented over time by specific Oracle products. As stated by Oracle Corporation, the goals of this strategy include:

• Scalability: A principal goal of the NCA is to overcome many of the limitations associated with client/server applications such as performance, administration, and deployment. For instance, by enabling the deployment of Web-based applications, the NCA significantly reduces the administration of client machines; a network administrator no longer needs to worry about the logistics of installing the latest version of an executable program and its associated libraries on hundreds of PCs.
• Portability: The goal of the NCA is to support enterprise software development, regardless of programming language, computing platform, or operating system. The use of Java is central to this goal. Java offers developers the possibility of writing software once and deploying it in a variety of computing environments.
• Interoperability: The NCA assumes that customers want the flexibility of choosing separate components, regardless of vendor, and expecting them to integrate; a customer might want to use the Oracle database server, a Netscape Web server, and a combination of Microsoft Windows 95 and Mac clients. By adhering to two common standards—CORBA 2.0 and HTTP/HTML—the NCA supports a heterogeneous environment.
• Support for component-based software development: Oracle Corporation has stated that the NCA will support the CORBA 2.0 specification, which addresses the use of distributed objects, regardless of their location on the network—client, application server, or database server. This support will be implemented in future releases of Oracle products.

Let's examine some of the benefits provided by the CORBA 2.0 specification.

CORBA

CORBA is the acronym for the Common Object Request Broker Architecture which is an architecture and specification produced by the Object Management Group, an industry consortium that was established in 1989. The current version of CORBA is 2.0, which was initially released in July 1995 and updated in July 1996. The principal goal of CORBA is to foster the use and integration of objects, regardless of the language used to construct the object and the operating system where it resides. CORBA accomplishes this goal through the use of an Object Request Broker (ORB) which is a piece of software that handles requests for object services. You can think of an ORB as an object bus. There are a number of ORB vendors, including Iona, Visigenic, Sun, HP, and IBM.