Oracle Application Express Release 4.2.6.00.03 is installed by default in Oracle Database 12c Release 1 (12.1). One of the major new capabilities introduced in Oracle Database 12c is Multitenant Architecture. [Please review the Multitenant Architecture on OTN to learn about this new architecture]
When you install Oracle Database 12c Multitenant Architecture, Oracle Application Express is installed into the multitenant container database by default. A single multitenant container database can have up to 252 pluggable databases (PDBs). The container database root (CDB$ROOT) includes an APEX_040200 schema which holds all of the common objects required for Application Express, including the Application Express engine packages, processes, functions and views. Therefore, there is only a single instance of these common objects across the whole database installation. The Application Express common objects, stored in the multitenant container database, are accessed from each PDB using meta-data links. Each PDB also includes an APEX_040200 schema which holds the Application Express meta-data tables for that specific PDB. These local tables ensure that the Application Express application definitions are maintained independently in each PDB. Each PDB must have a Web listener defined and is managed individually using the standard Oracle Application Express Instance Administration.
In the standard configuration, the version of Application Express installed can be updated for the multitenant container database and all pluggable databases using a single script. All pluggable databases *must* run the same version of Application Express. However, Application Express is unique amongst Oracle database options in that it can be removed from the multitenant container database and re-installed locally into a single pluggable database. This flexibility allows a single Oracle Database 12c Multitenant Architecture to run different versions of Oracle Application Express in each PDB. Once uninstalled from the multitenant container database you also have the option to reinstall Application Express into the container database. This option will enable you to re-install a runtime only configuration of Application Express into the multiteant container database.
NOTE: Oracle recommends downloading and installing the latest version of Oracle Application Express before starting new development.
The following collateral is specific to Oracle Application Express 4.2 and above in Oracle Database 12c:
In additional to the changes made to Oracle Application Express 4.2 to work within the new Oracle Database 12c Multitenant Architecture, additional changes have also been made to accommodate some other Oracle Database 12c new features. The new features which may be important to Oracle Application Express developers in Oracle Database 12c include:
$ORACLE_HOME/core/collection_member_resize.sqlto update the VARCHAR2 columns from 4000 to 32,767 characters.