The computer systems have increasingly invaded our daily lives from the simplest application as audio files reading to the most critical one as cars and airplanes. For critical systems, the validation by the formal verification is required. This Thesis concerns this area of research and aims to ensure the betterment of UML language, which is the de facto standard, with formal semantics for verification finality. For the first part, we have analyzed and revised the theoretical foundations the existing formal verification methods used UML, their profiles and the basic concepts of the Petri nets (PNs). For the second part, we have created a novel hierarchical approach to formalize the Interaction Overview Diagrams (IOD). Based on this idea, we...