Strict Profiles. Why and How

The definition of a clean profile mechanism will play a crucial role in the UML's future in terms of how useful it will be to modellers and how well tool vendors may implement the new facilities. Unfortunately, in an attempt to restrict profile definitions to a single meta level, the currently proposed profile mechanism violates some of the basic premises of meta-modeling, as captured by the doctrine of strict metamodeling. In particular "predefined" modeling elements are currently specified exclusively at the meta-model level in the UML's four-level model architecture, and therefore can be applied solely through the mechanism of meta-instantiation (either implicitly in the form of stereotypes or explicitly through class instantiation). We identify the problems associated with such a restriction and explain why regular model level inheritance also has an important role to play in the definition of predefined modeling elements. We also identify the fundamental differences and relationships between the two mechanisms when used for the definition of UML profiles and provide guidelines as to which mechanism should be used under which circumstance. We conclude by showing how inheritance and instantiation should be used together to define UML profiles in the context of a strict metamodeling framework.