This should not be an issue, although it has generated a disproportionate amount of discussion.
The object-oriented designer and programmer are accustomed to creating object classes as necessary to solve particular problems. Even if they are presented with a conceptual data model as a starting point, there is nothing in their normal work practices to keep them from at least adding system-oriented classes. Indeed, many of the classes are only defined to last for the life of the program’s execution. Only “moral persuasion” discourages them from changing the architectural model’s class structure.