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Server Extensions

There are three basic techniques for executing applications on the server to dynamically generate Web pages:

The first two are languages that the WebServer can cause to be executed. The last is an HTML technique for passing execution to another process at a certain point in the scanning of a Web page, and embedding the output of that process in the calling page. LiveHTML can also execute programs, but its programs are written in some language, such as Perl for Unix or Visual Basic for Windows NT, that is executed by the OS itself rather than the WebServer.

Generally speaking, you can combine these techniques. For example, the Java Interpreter can execute PL/SQL in the database.

The PL/SQL Agent and the Java Interpreter can use either of two interfaces: WRB or CGI. Which interface is used is determined by the mapping of the "file" the URL requests; this mapping is part of the WebServer configuration.

How URLs Specify Applications

Once the Listener has determined that a URL specifies that an application is to be executed on the server, it interprets the URL to extract path information and arguments to be passed to the application on start-up.

URLs that specify applications are split into three different parts:

The syntax is as follows:

virtual_path extra_path_information?query_string

Here are the explanations of the syntax components:

virtual path
This is similar to a path you would use to access a regular document or image. That is, it is a pathname that identifies the application that you want executed.

extra path information
This is optional additional information embedded in the URL after the pathname. This consists primarily of various environment variables that you can use to pass information to the application.

query string
This is another optional part of the URL. This is used to directly supply parameter values (as opposed to environment variable values) to the requested application. The parameters are specified in the following form:

<parameter name>=<value>

Example of a URL Invoking an Application

This section provides an example of a URL that invokes a PL/SQL Agent to access the database. Here is the URL in question:

http://www.nhl.com:8080/ows-bin/nhl/owa/hockey_pass?person=Gretzky

  1. The substring http://www.nhl.com:8080 in the above URL signals the Web browser to connect to the www.nhl.com host's port 8080 using the HTTP protocol.

  2. When the Oracle Web Listener that is running on www.nhl.com receives the request, the substring /ows-bin/nhl/owa signals the Web Listener to connect to the PL/SQL Agent instead of returning a file to the browser as it normally would have done with a static HTML document.

  3. The URL is processed as follows:

    The Listener is configured so that the string /ows-bin/nhl/owa causes it to invoke the WRB Dispatcher. The WRB Dispatcher understands "owa" to mean it should pass execution to a WRBX interfaced to the PL/SQL Service. It passes the WRBX the following information in the form of CGI environment variables (For the sake of compatibility, WRB understands CGI environment variables):

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This document was last modified at 03:55pm PST on March 27, 1996.

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