The function of good software is to make the complex appear to be simple. - Grady Booch

[A class category is] a collection of classes, some of which are visible to other class categories, and others of which are hidden.

#The development of the Model Driven Architecture (MDA) standards by the Object Management Group (OMG)

#A proposed profile of UML—Executable UML—supports creating a complete and implementation-neutral self-contained expression of application functionality. Steven J. Mellor and Marc J. Balcer define this profile in their book Executable UML: A Foundation for Model-Driven Architecture