The Application Express engine renders applications in real time from data stored in database tables. When you create or extend an application, Oracle Application Express creates or modifies metadata stored in database tables. When the application is run, the Application Express engine then reads the metadata and displays the application. Application Express lives completely within your Oracle database. It is comprised of nothing more than data in tables and large amounts of PL/SQL code. The essence of Oracle Application Express is approximately 215 tables and 200 PL/SQL objects containing 300,000+ lines of code.
To provide stateful behavior within an application, Oracle Application Express transparently manages session state in the database. Application developers can get and set session state using simple substitutions as well as standard SQL bind variable syntax.
To access the Oracle Application Express engine within the Oracle database you must configure the Oracle HTTP Server(Apache) containing the mod_plsql plug-in . The plugin functions as communication broker between the Web server and the Oracle Application Express objects in the Oracle database. This maps browser requests into database stored procedure calls. The following graphic illustrates the Oracle Application Express architecture using Oracle HTTP Server and mod_plsql.
