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Developing Web Applications with PL/SQL

If you think that only new languages such as Java and JavaScript can do network operations and produce dynamic Web content, think again. PL/SQL has a number of features that you can use to Web-enable your database and make your back-office data interactive and accessible to intranet users or your customers.

This chapter discusses the following topics:

PL/SQL Web Applications

PL/SQL Gateway

PL/SQL Web Toolkit

Generating HTML Output from PL/SQL

Passing Parameters to a PL/SQL Web Application

Performing Network Operations within PL/SQL Stored Procedures

Embedding PL/SQL Code in Web Pages (PL/SQL Server Pages)

Enabling PL/SQL Web Applications for XML

Developing Web Applications with PL/SQL 13-1

PL/SQL Web Applications

PL/SQL Web Applications

Web applications written in PL/SQL are typically sets of stored procedures that interact with Web browsers through the HTTP protocol. A set of interlinked dynamic HTML pages forms the user interface of a web application.

When a Web browser user visits a Web page, follows a hypertext link, or presses a Submit button on an HTML form, a URL is sent to the Web (HTTP) server, which causes the database server to run a stored procedure. Information the user provides in an HTML form is encoded in the URL. The URL also encodes information to identify which procedure, in which database, to call. The Web server passes this information along to the database as a set of parameters for the stored procedure.

The stored procedure that is invoked from a URL calls subprograms from the PL/SQL Web Toolkit. Typically, some of these subprograms, such as Htp.Print, prepare an HTML page that is displayed in the Web browser as a response to the user.

This process dynamically generates Web pages. Code running inside the database server produces HTML on the fly, so the generated Web page can vary depending on the database contents and the input parameters.

Dynamic generation of HTML is to be distinguished from dynamic HTML (DHTML). With DHTML, code in JavaScript or some other scripting language is downloaded to the browser along with HTML code, and this script code is processed by the browser.

DHTML can be coded by hand, so that it is static code, or it can itself be generated by program. That is, the generation of Web pages using a database can be combined with downloading JavaScript or other DHTML script code. A PL/SQL Web application can dynamically create complex DHTML that would be tedious to produce manually. A typical stored procedure might print some header information, issue a database query, and loop through the result set, formatting the data in an HTML list or table.

This program flow is very similar to a Perl script that operates on a text file. CGI scripts and programs running on a Web server are often used to dynamically produce Web pages, but they are usually not the best choice for interacting with a database. Using PL/SQL stored procedures has the advantage of providing all the power and flexibility of database processing: it supports DML statements, dynamic SQL, and cursors. It also eliminates the memory overhead of forking a new CGI process to treat each URL.

A Web browser-based application can be implemented entirely in PL/SQL using the following Oracle Database components:

13-2 Oracle Database Application Developer's Guide - Fundamentals

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