Oracle Application Express 3.2 - The Essentials and More: Develop Native Oracle database-centric web applications quickly and easily with Oracle APEX

The term Web-based appears in the description of both the development tool and its product the APEX application. We are using a Web browser to both develop and run our applications. The advantages are obvious. Web browsers are installed, almost by default, on most of the workstations we are using, independently of the workstation hardware or operating system. It means that on the client side, we don't need anything else to start developing with APEX, or to run APEX applications. Moreover, it means very easy access to our applications, both internally using Intranet or externally, using the Internet. If we add all the modern smart phones and other PDAs on the market today, which include built-in Web browsers, we'll come to the conclusion that the range of options to access our APEX applications is very wide.

Another important advantage when using a Web browser is the ability to free us from hardware and local operating system dependencies. As the APEX Application Builder actually generates HTML code, we (as developers) don't have to worry about the hardware specifications, or the local operating system our end users will be using, to run our APEX application. As long as they have access to an HTML supporting Web browser, we are covered.

However, Web based application development can also be a drawback. Unfortunately, not all Web browser manufacturers have fully adopted all the international standards in this field. As a result, there are cases in which different Web browsers will display the same code page differently. The variety of Web browsers in the market today, like Internet Explorer, Firefox, Chrome, Opera and Safari, just to name a few, support and implement HTML, XHTML, CSS and JavaScript versions and levels, in different ways and styles. There are known cases where even the same Web browser brand, but in different versions, or across local operating systems, delivers different results with the same code. We need to be aware of this, and take actions to resolve it if we want to ensure cross-browser compatibility code for our applications (which will apply to greater numbers of potential users). Sometimes we need to take hard decisions and waive the support of certain web browsers in order to keep our code simple and maintainable.

A list of supported Web browsers can be found in the APEX release notes. For version 3.2, which is the latest APEX version at the time of writing this book, it can be found at http://download.oracle.com/docs/cd/E14373_01/relnotes.32/e13365/toc.htm#BGBCEGBI

APEX, in all its previous forms, was always designed to operate in the Web environment. The final product of the APEX Application Builder is HTML code that can be run directly on any Web browser that supports the HTML 4.0 and above standard. APEX Application Builder also incorporates special features into generated applications, as a direct result of operating in the Web environment. Further on, we will discuss APEX architecture and its main features, but for now we will mention session state and Optimistic Locking, as distinguished Web environment features which help us overcome the stateless nature of this environment.

The APEX Application Builder fully supports CSS (Cascading Style Sheets) and JavaScript, as integrated components of APEX applications. That includes built-in CSS files as part of a wider page layout and format mechanism, which we'll address later in the book, and a JavaScript library. The JavaScript library also includes, among a variety of general and APEX related functions, an AJAX (Asynchronous JavaScript and XML) framework. This allows even novice developers to utilize this advanced technology, and produce high quality applications, compatible with the latest trends in the market like Web 2.0, etc.

APEX was designed to produce applications that store, retrieve, manipulate, and display data, from Oracle Databases. This means that if your application's main logic doesn't revolve around data manipulation, it may be that APEX is not your optimal application development tool. However, if data manipulation is at the heart of your application, APEX could be your best bet.

APEX is actually a collection of PL/SQL packages, which "live" inside the Oracle database. It means that APEX automatically inherits all the outstanding features, often mentioned with regards to the Oracle database environment: high performance, robustness, reliability, enhanced security, scalability, and more. In addition, APEX can natively utilize the very rich SQL and PL/SQL environment, including the built-in packages that the Oracle database has to offer, and use them to manipulate the data in the optimal ways a RDBMS can offer.

Moreover, APEX can utilize special functionality features that are included in the various database versions and editions, like Oracle XML DB, Oracle Text, and Oracle Multimedia.

Another advantage in this context is that, like the client side which relies on Web browsers to gain hardware independence, (alongside operating system independence), the APEX engine relies on the database platform for the same purpose. As long as we have a proper running version of an Oracle database, starting with Oracle database 9.2.0.3 and above (including the free version, Oracle XE), we can ignore the hardware and operating systems aspects of the server.

APEX is a declarative tool. It means that we, as developers, concentrate more on the "What needs to be done", and less on the "How to do it". Think, for example, about SQL. In a SELECT statement, when we are using the ORDER BY clause, we are actually telling the database what we need - a sorted data result set, but we don't tell it how to actually do the sorting. In fact, the entire SELECT statement, just like SQL itself, is a declarative statement. In APEX, we are telling the Application builder that we need to lay out an HTML item on the page, or retrieve certain records from the database, and the APEX engine generates the proper code for doing that, both on the server side and the client side.

Working declaratively in APEX means that we are not generating traditional (3 GL) program code. Instead, we are working with a series of wizards and property sheets, which allows us to define all the metadata we need in order to generate an application page's code. APEX includes sets of pre-defined wizards, supported HTML objects, supported database objects and data types, page rendering options and procedures, after submit processes and DML options, navigation and branching options, and more. We can use all of these to declare our application page's forms, reports, charts, etc., with their layouts and application/business logic. The APEX engine translates it all into an HTML code for the client side, and SQL and PL/SQL code for the server side. Whenever the predefined options don't give us the exact solution we need, APEX allows us to use our own SQL and PL/SQL code for the server side, and HTML/XHTML, CSS, and JavaScript code, for the client side. As mentioned before, it also allows us the use of AJAX technology, within a built-in framework, to query the server side, while running on the client side without submitting the page.

APEX provides us with a full development environment, allowing us to develop, test, and deploy our applications. APEX includes three modules: Application Builder, SQL Workshop, and Utilities.

APEX was designed with globalization, localization, and NLS (National Language Support) in mind. To begin with, the APEX interface is translated into nine languages, other than English. The languages are German, Spanish, French, Italian, Japanese, Korean, Brazilian Portuguese, Simplified Chinese, and Traditional Chinese.

APEX can utilize all the globalization, localization, and NLS features that the Oracle database has to offer, and add some of its own. The Application Builder Shared Components module includes a Globalization section, which allows us to define relevant parameters for globalization, localization, and NLS. It also includes a wizard to guide us through the process of translating our entire application into secondary languages.

APEX takes into account the client side NLS settings when dealing with the import and export of data into and out of the database. It also takes into account the database NLS settings, in order to properly sort data, display dates, number format (e.g. decimal point or comma) and the local currency, among others.

APEX supports the XLIFF (XML Localization Interchange File Format) standard, which allows us to translate an entire APEX application into any language we need, without re-writing the application code. APEX provides a built-in mechanism to simultaneously run the same application in multi language User Interfaces, giving us several options to determine the application language, including the option of matching the APEX application language to the end user's browser language preferences. Moreover, if we need to support a language which is not included in the native supported languages list, this mechanism will allow us to specifically translate the built-in APEX engine strings and messages into that language, allowing us to develop and support APEX application in any language that our database can support.

Throughout this book, we will devote special attention to globalization, localization, and NLS issues in the APEX environment, including RTL (Right-To-Left) support examples.

The core of APEX is a collection of PL/SQL packages, written using the PL/SQL Web Toolkit, and several hundred database tables, in which all the metadata regarding developed applications are stored.

The PL/SQL Web Toolkit is a collection of Oracle supplied database packages, which allow us to produce Web page code, directly in the database, using PL/SQL stored procedures. During run-time, and in real-time, the APEX engine queries the metadata tables and retrieves all the relevant information for a specific application page. Next, it uses the PL/SQL Web Toolkit to generate the application page's HTML code. This page's code also includes the proper linkage to the CSS and JavaScript resources that support proper page functionality, layout, and styles. Some internal tests run by the APEX development team, showed that the APEX engine performs all the real-time rendering processes, with an average overhead of less than 0.04 seconds per page. Pretty impressive in my opinion, and the APEX engine includes a server side caching mechanism, that can help us reduce that further.

It is important to understand that although the final product of APEX Application Builder is an HTML page code, no static files with any related HTML file extensions, are stored on the server. Each page is created upon demand a specific URI request. That, of course, gives us considerable flexibility with constructing the pages, e.g. the same page can be displayed somewhat differently for various users, or include conditioned components, depending on the user's security privileges, or role in the company, etc.

So, on one side we have the APEX engine, a collection of PL/SQL packages, running inside an Oracle database, and on the other side we have the application user, using a Web browser. How can we connect, and communicate between the sides? As we are in a Web environment, we are going to use the HTTP protocol, implemented in two technologies.

The first way is by using the Oracle HTTP Server (OHS) technology. OHS is based on the well-known (open source) Apache HTTP server, in its 1.3 or 2.0 versions. What interests us, for the APEX environment, is the Oracle plug-in module for this HTTP server, called mod_plsql.

OHS, with the mod_plsql module, is located between the client's Web browser and the Oracle database server. The mod_plsql module communicates with the database by mapping the Web browser request into PL/SQL stored procedures in the database. In turn, the PL/SQL stored procedures can manipulate the data in the database tables and generate HTTP responses, which can include HTML code, to be displayed on the client Web browser.

In order to communicate with the database, mod_plsql is using a DAD (Database Access Descriptor) file, which contains configuration parameters on how to connect with the database, which user and password to use, NLS parameters, and others.

The second technology to implement the HTTP communication protocol utilizes the Embedded PL/SQL Gateway running on the XML DB HTTP server, which is an integrated feature of the Oracle Database. Using the DBMS_EPG package, the Embedded PL/SQL Gateway can implement the core functionality of the OHS mod_plsql module, without installing it. This technology was first supported by APEX in the embedded version (2.1) of the Oracle XE database. Today, it's also supported by APEX 3.0 and above versions, running on Oracle 11g databases. APEX 3.0, which uses the embedded PL/SQL gateway, is installed by default as part of the 11g database installation process, and can be upgraded to any higher APEX version.

APEX is a RAD tool, running inside an Oracle database. Using a Web browser, it allows us to develop, test, and deploy a Web based, data centric application, in a declarative manner.

Although APEX is a declarative tool, we need to be familiar with some other programming technologies and resources, in order to optimally utilize it. That's in the next chapter.