Understanding Oracle Application Express Architecture

Oracle Application Express lives completely within your Oracle database. It is comprised of data in tables and PL/SQL code.

Whether you are running the Oracle Application Express development environment or an application you built using Oracle Application Express, the process is the same. Your browser sends a URL request that is translated into the appropriate Oracle Application Express PL/SQL call. After the database processes the PL/SQL, the results are relayed back to your browser as HTML. This cycle happens each time you either request or submit a page.

The application session state is managed in the database tables within Application Express. It does not use a dedicated database connection. Instead, each request is made through a new database session, consuming minimal CPU resources.

About Apache and the Embedded PL/SQL Gateway

The version of Oracle database you use determines how the URL is translated:

Versions prior to Oracle Database 11.1 require Oracle HTTP Server (Apache) with mod_plsql. The following graphic illustrates that architecture.

Description of the illustration arch.gif

With Oracle Database 11.1 or higher or Oracle Database 10g Express Edition, you can remove Oracle HTTP Server (Apache) from the architecture and replace it with the embedded PL/SQL gateway. The following graphic illustrates the architecture using the emedded PL/SQL gateway.

Description of the illustration arch_epg.gif

The embedded PL/SQL gateway provides the Oracle database with a Web server and also the necessary infrastructure to create dynamic applications. The embedded PL/SQL gateway runs in the XML database HTTP server in the Oracle database and includes the core features of mod_plsql, but does not require the Oracle HTTP Server powered by Apache. Inclusion of the embedded PL/SQL gateway simplifies the architecture and eliminates the middle tier entirely.

About the Application Express Engine

The Application Express engine renders and processes pages. It also performs these tasks:

session state management
authentication services
authorization services
page flow control
validations processing