Another important part of CORBA 2.0 is the specification for Interface Definition Language (IDL), which provides a language-independent description of the services provided by an object. The ORB vendors provide software that will generate language-specific bindings from IDL. The intent of CORBA 2.0 is to reduce the external specification for an object to its IDL. A developer doesn't need to know about the language used to implement an object or the operating system on which it was developed; everything that a developer needs to know about an object is contained in its IDL specification. IDL is a subset of the proposed C++ ANSI specification with extensions to support the invocation of object services.

CORBA 2.0 also includes a specification for Internet Inter-ORB Protocol (IIOP). This protocol specifies the communication mechanism, via TCP/IP, that allows one ORB to communicate with another ORB. Essentially, IIOP is a mechanism whereby a client on a computing platform can issue a request for a service from object abc which is handled by an ORB. Acting as a client, object abc issues a request, sent via TCP/IP, for a service from object xyz which is managed by an ORB on a different computing platform.

Components of the Network Computing
Architecture

Because a picture is worth a thousand words, please look at Figure 21.11 for a diagram of the Network Computing Architecture. As you can see, the components of the NCA are as follows:

• The Oracle Universal Server
• The Oracle Universal Application Server
• Cartridges that may interface with the client, application server, or universal server
• The Inter-Cartridge Exchange that allows cartridges to communicate with one another
• A client that may be a PC, a Mac, or a network computer

Cartridges

As envisioned by the NCA, a cartridge is a software component that interfaces with the client, application server, or the database itself. The purpose of a cartridge is to provide a specialized capability that is made available to other components and cartridges in the NCA. For example, an organization might develop a cartridge to handle the processing of some external data feed such as commodity prices. A cartridge can utilize the services that are provided by the NCA such as installation, registration, instantiation, administration, and security. You can write a cartridge in many different languages such as Java, C++, or PL/SQL.

Figure 21.11.
Diagram of Network
Computing Architec-
ture.

Inter-Cartridge Exchange

The NCA includes a component called the Inter-Cartridge Exchange (ICX) that acts as a clearinghouse for the services provided by cartridges wherever they exist on the network—on the client, on the application server, or on the database server. In addition to functioning as an ORB, the ICX also integrates the NCA with the Microsoft Component Object Model (COM) so that ActiveX clients can communicate with NCA cartridges. The ICX will also provide integration with Java components and legacy system interfaces. If you are using Oracle server version 7.3.3 or above, you can communicate with the ICX via the PL/SQL Cartridge.

Summary

In this final lesson, the key concepts to remember are the following:

• Oracle Web Application Server can be used to provide access to an Oracle database from a Web browser.
• The components of the Web Application Server are the Web Listener, the Database Access Descriptor, the Web Request Broker, and cartridges for various languages.
• Developer/2000 for the Web allows an Oracle Forms or Reports application to be deployed either as a client/server application or a Web application.

• Developer/2000 for the Web utilizes a Forms Server which translates the contents of an .FMX or .RDF file into calls to various Java components.
• The Network Computing Architecture is Oracle's strategy for the future of commercial software development. It emphasizes support for open standards such as CORBA 2.0 and HTTP/HTML.

Q&A

Q Can the Web Application Server be used to access a non-Oracle database?
A Yes. This can be accomplished through the use of a gateway. Oracle offers gateway products for popular databases such as DB2 and Sybase. Another alternative is to use the ODBC cartridge to access a non-Oracle database, assuming that an ODBC driver is available for the non-Oracle database.

Workshop

The purpose of the Workshop is to allow you to test your knowledge of the material discussed in the lesson.

Quiz

1. What is the role of the htp and htf PL/SQL packages?
2. True or false? The Network Computing Architecture is available only for Sun Solaris and Microsoft Windows NT Server.