Reference classes are classes that do not participate in the code generation process. They are automatically created by reverse engineering when classes in the reverse engineered set of files have inheritance relationships with classes that are not defined in the code that is being reverse engineered. Reference classes complete the relationships, but have no content (attributes or operations defined), and no code is generated for them.
Once you have your library of reference classes, you can use them as components in creating a new system by:
You can inherit or create associations to the reference class, and UML Modeling knows not to generate the source files for the reference class.