Databases Reference
In-Depth Information
There are three options for listeners for APEX: an embedded PL/SQL
listener, a mod that can be used with Apache, and the APEX Listener
that is used for the Oracle Database Cloud Service. Some capabilities
of the overall environment discussed here, such as RESTful Web Serv‐
ices, are dependent on the use of the APEX Listener. The Database
Cloud Service includes the APEX Listener.
APEX is a declarative development environment. When you create applications, pages,
or components that are shared across pages or Web Services, APEX uses wizards to
collect metadata. When a particular page is requested by a user, a PL/SQL procedure
retrieves the metadata and constructs the HTML page based on that metadata.
This architecture has two important implications for APEX applications. The first is
that applications are just a set of metadata, which means you can move them from one
Oracle instance to another with a simple SQL script. As long as you have the metadata
repository tables and the PL/SQL procedures installed, the application will run on the
target instance.
The second implication is more profound. Since pages are built dynamically from met‐
adata, there is absolutely no deployment process for APEX applications. This architec‐
ture, coupled with the high productivity of a declarative development process, leads to
the capability to do
iterative development
. You are able to not only create applications
rapidly, but you can change them in real time while working with users. The interaction
with users and the high productivity are well suited to the world of cloud computing.
Development with the Database Cloud Service
As mentioned above, Application Express has been around since 2004, with a fairly large
and very involved user community. Over the years, Application Express has become a
very rich and robust development environment.
Since APEX is based in the Oracle Database, you can use the full power of SQL and PL/
SQL to define data interactions and extend application logic, respectively. Although you
do not have to know either of these interfaces to create and deploy APEX applications,
the ability to use them means that you can build virtually any type of application with
APEX. Since APEX applications are made up of HTML pages, you can also use features
from HTML, including formatting and JavaScript, in your APEX applications, although
you do not need to know HTML to create applications either.
Each APEX page includes metadata to control the appearance of the page and any special
processing for the page, and typically uses a set of shared components across pages.
