Abstract. Many real-time systems use runtime structural reconfiguration mechanisms based on dynamic creation and destruction of components. To support such features, UML-RT provides a set of modeling concepts including optional actor references and multiple containment. However, these concepts are not covered in any of the current formal semantics of UML-RT, thus impeding the testing and formal analysis of realistic models. We use AsmL to present an executable semantics covering dynamic structures and other important features like run time schedulability. The semantics is parametrized to capture UML-RT semantics variation points whose decision choices depend on the special implementation in a vendor CASE tool. We have built several various implementations of those variation points, including the one as implemented in the IBM Rational Rose RealTime (Rose-RT) tool. Finally, we illustrate how the proposed executable semantics can be used in the analysis of a Rose-RT model using the Spec ...