Profiles in a strict metamodeling framework

If the UML is to continue to meet the expectations of its ever-growing user community it is essential that it offer a simple and coherent mechanism for users to tailor the language to their specific needs. However, current UML extension approaches are not only unnecessarily limited in the capabilities that they provide, but also break some of the fundamental tenets of metamodeling in a multi-level framework. In particular, they are all based on the assumption that instantiation, in one form or another, is the only mechanism by which end users can apply predefined model elements in their own applications. In this paper we identify the problems associated with this limitation and explain why inheritance is also important for allowing users to apply predefined model elements. We point out the fundamental differences and relationships between instantiation and inheritance for defining UML profiles and provide guidelines as to which mechanism should be used under which circumstances. We conclude by describing why both mechanisms should be utilized in the definition of UML profiles in the context of strict, linear metamodeling frameworks.