All application components are objects that are created using the OpenROAD system classes. For example, a frame is an object of the FrameExec system class, and a button field is an object of the ButtonField system class.

The class of an object defines the attributes you can read and set for that object. For example, the ButtonField class includes a BitmapLabel attribute that lets you specify an image as the button's label. For more information about how to read and set these attributes, see How You Can Set and Get Attributes (see How You Can Set and Get Attributes).

The class of an object also defines the methods that you can invoke to manipulate the object. For example, the EntryField class includes a MarkAllText method that you can use to highlight the text in an entry field. For more information about how to invoke a method on an object, see How You Can Invoke Methods (see How You Can Invoke Methods).

Following an object‑oriented model, the OpenROAD system classes use an inheritance hierarchy in which each subclass inherits the attributes and methods defined for all its superclasses. When you create your own user classes, you can structure them into an inheritance hierarchy. For more information about class hierarchies, see Inheritance (see Inheritance).