A descriptor class framework fully support a "start-from-class" approach, which defines a descriptor via a set of programmable classes defined in an object-oriented programming language. While the persistent form of a descriptor of a deployed software component is a file, the developer of an application using software component may view the descriptor as a set of programmable descriptor classes. A set of classes can be generated from a descriptor based on a set of construction rules and vise versa. Each class can be annotated, validated and customized. The descriptor class framework is also capable of determining the differences between two versions of a descriptor and notifying the changes to a corresponding class via events to a listener registered with the class.