  Thanks to its graphical notation and simplicity, Unified Modeling Language
(UML) is a de facto standard and a widespread language used in both industry
and academia, despite the fact that its semantics is still informal. The
Interaction Overview Diagram (IOD) is introduced in UML2; it allows the
specification of the behavior in the hierarchical way. This paper is a
contribution towards a formal dynamic semantics of UML2. We start by
formalizing the Hierarchical use of IOD. Afterward, we complete the mapping of
IOD, Sequence Diagrams and Timing Diagrams into Hierarchical Colored Petri Nets
(HCPNs) using the Timed colored Petri Nets (timed CP-net). Our approach helps
designers to get benefits from abstraction as well as refinement at more than
two levels of hierarchy which reduces verification complexity.
