The MVC approach is geared towards separation of business and presentation logic. It has evolved in the desktop application programming but it is most suitable for web applications. The idea behind MVC is simple - every application can be split into three parts:
- the data model that represents the data, their structure and internal links, possibly with methods of changing, creating and deleting pieces of that data in case of object-oriented representation of business entities;
- the controllers that process the input from user and alter or retrieve requested data;
- the views that display the user actual results of actions taken by the controllers.
In Freeform Framework, the remote user that interacts with the application over the HTTP protocol, always interacts with the controllers. The controllers in Freeform are called Actions to reflect the fact that each controller is the possible action of the user.
The Actions are interacting with the model which can be anything from simple flat-file-based database to complex relational databases residing on SQL servers or even object databases. Also Actions are responsible for preparing correct views, or responce documents, to be returned to the user as a result of the Action execution. Generally, responce documents will be regular HTML files, however, you can easily generate WML/XML content, images, audio files or simple plain text.
In Freeform, the responce documents are implementations of the Document interface. These objects are created by Actions, possibly filled with some variables to be returned in form of text, graphics or multimedia, can contain input forms and links that trigger other Actions.
The client requests some Action to be processed on the server by clicking on hyperlinks or submitting a form. Each Action queries or alters the model and prepares the resulting view (usually it means instantiating a Document implementation instance, setting some variables in the Document and returning the Document to the user).
The MVC approach as implemented in Freeform Framework, looks like this:
As you can see, all requests are handled by Actions that may query the data model and pass the results to the initialized documents. The responces are brought back to the client and the entire loop may begin again if the user clicks on a link or submits a form.