OAF - Introduction and MVC Concept

Oracle Application Framework (OAF)

Introduction of OAF

* Oracle Application Framework (OA Framework) is the Oracle Applications development  and  
   deployment platform for HTML-based business applications. 

* OA Framework consists of a set of middle-tier run time services and a design-time extension to
   Oracle JDeveloper called Oracle Applications Extension (OA Extension).

OA Framework:

• Regions are created as XML but then loaded into Database into JDR% tables.
• The meta-data is defined as XML at design time, which is latter loaded into JDR* tables in the database.
• Completely integrated within jDeveloper for design and development purposes.
• MVC Industry Standard Architecture.

Disadvantages

1. Declarative design of screens. What you see is not what you get for layout
2. No drag and drop  for designing layout of the Page.
3. Oracle does not provide access to Java source code for OA Framework or  products. You should consider the Developer's guide and available Javadoc for the classes

Architecture of OAF
OA Framework is based on the industry-standard J2EE MVC design pattern. Developers manipulate the application's metadata using Oracle JDeveloper OA Extension, while OA Framework uses the most efficient manner to execute the application. The MVC architecture is a component-based design pattern with clean interfaces between the Model, View, and Controller. 

• The Model is where the application implements its business logic. 
• The View is where the application implements its user interface and the 
• Controller is where the application handles user interaction and directs business flow.

OA Extension offers the following design time tools: 

1. UML tools to model and generate business logic.
2. Guided user interface (and visual editors in a future release) to lay out client user interfaces.
3. Code generation for Controller classes.

The OA Framework Model is implemented using Oracle Business Components for Java (BC4J). BC4J provides optimized, ready-to-use implementations of the J2EE design patterns that developers otherwise would have to code, debug, and test by hand. By leveraging BC4J's combination of tested code and productivity tools inside the Oracle JDeveloper IDE, development teams can focus immediately and only, on writing business logic and user interfaces instead of on designing, coding, and debugging handcrafted application "plumbing" code. 

The OA Framework View is implemented using UI XML (UIX). UIX uses XML to describe the 
components and hierarchy that make up an application page. UIX also provides run time 
capabilities to translate that metadata into HTML output so that it can be shown on a Browser or 
a mobile device. The metadata used to describe the UI is loaded into a database repository, called 
Meta Data Services (MDS), at deployment time and optionally at design time as well. 

User- and application-driven interactions are handled by the OA Controller, which is a pure Java 
class implementation. Simple page flows (such as a 2-step transaction) are implemented directly 
into the Controller object; others are implemented using Oracle Workflow. In a future release, 
business flows will be implemented in a declarative manner similar to that used to define model 

and view objects.

Whenever there’s a request for a new page submitted then the OA framework first read the metadata associated with that page from the XML files stored in the MDS database repository And creates a web bean hierarchy(Java Beans) controlled by the controller. Now,when the page processing completes then the code written in the beans get converted to the html code n being sent to the html browser by the UIX framework.