The model refers to the business logic part of the application. This consists of application classes and script includes. All files of the model are stored in /model directory.

An Application Class refers to any PHP class that contains the business logic of the application and is a part of the model. Application classes can be created and managed directly through the Opendelight IDE. However, you can also edit these classes in your favourite code editor. These classes are located in the /model/class directory.

#### NOTE

1. The filename of an Application Class should be exactly the same as the class name but should have the extension as .cls.php. There should be no white space in the class name or in the corresponding filename.
2. Do not create the name of Application Class equal to the Opendelight library class which always starts with Delight_
3. There is no need to include Application Class files as the classes are autoloader.

A Script Include refers to any PHP file that contains the business logic of the application and is a part of the model. This file is included in an event to execute the respective business logic. Script Includes can be created and managed directly through the Opendelight IDE. However, you can also edit these files in your favourite code editor. These files are located in /model/script directory. The filename of a Script Include should have the file extension as .inc.php.

The other thing that you can manage about the model is the Configuration Variables of the application. While developing an application, we tend to use a number of magic numbers. Ideally, we store these in a separate file, and in turn, include them every time within the application. With the Opendelight, we do not need to do any such effort; rather we create these as configuration variables on the Opendelight IDE and then use them as a property (date type is an associative array) of $APP object, $APP->CONFIG, within the application. You can add a Configuration Variable by filling Variable Name, Description, and Value of Variable on the Opendelight IDE. You can arrange the display order of the created variables; however, this is just for display purpose on the Opendelight IDE (for readability of list of variables for developer), and do not have any other requirement during application development.