Variability within Modeling Language Definitions
  We present a taxonomy of the variability mechanisms offered by modeling languages. The definition of a formal language encompasses a syntax and a semantic domain as well as the mapping that relates them, thus language variabilities are classified according to which of those three pillars they address. This work furthermore proposes a framework to explicitly document and manage the variation points and their corresponding variants of a variable modeling language. The framework enables the systematic study of various kinds of variabilities and their interdependencies. Moreover, it allows a methodical customization of a language, for example, to a given application domain. The taxonomy of variability is explicitly of interest for the UML to provide a more precise understanding of its variation points. 
Maria Victoria Cengarle, Hans Gr\"onninger, Bernhard Rumpe
cs.SE