Specifying consistent subsets of UML

While increasing progressively its expressive power, UML has become more and more difficult to read and understand, especially for beginners. To teach the whole UML is not possible, therefore teachers only deal with a subset of UML. We present a framework for defining precisely a consistent subset of a language, allowing everybody to define his/her own subset. An extended example shows a way to simplify UML sequence diagrams. Our approach use standard UML tools; models in the simplified language are fully compatible with UML; model mapping between metamodels is done automatically from specifications based on marking with stereotypes; constraints are automatically translated from the simplified language to UML.