In a model-based development of software systems different views on a system are elaborated using appropriate modeling languages and techniques. Because of the unavoidable heterogeneity of the viewpoint models, a semantic integration is required, to establish the correspondences of the models and allow checking of their relative consistency. The integration approach introduced in this book is based on a common semantic domain of abstract systems, their composition and development. Its applicability is shown through semantic interpretations and compositional comparisons of different specification approaches. These range from formal specification techniques like process calculi, Petri nets and rule-based formalisms to semiformal software modeling languages like those in the UML family.