"Regarding executability, it is clear that from the hypothetical day when a UML virtual machine would be universally adopted, UML-based process models would have a real benefit. Process modelers supposed to be already familiar with UML diagrams would then simply have to draw their process models using their usual UML tools. They would then be able to test, execute and debug them as everyone does with her usual programming language. offers the potential to define such virtual machine thanks notably to the Activity and Action packages, which come with an operational semantics. Some ambiguities in this operational semantics (given in natural language in the standard), have however to be first fixed. This is one of the purposes of a recent initiative at the OMG, called Executable UML"