This book offers up a deep understanding of concepts and practices behind the composition of heterogeneous components. After the analysis of existing computation and execution models used for the specification and validation of different sub-systems, the book introduces a systematic approach to build an execution model for systems composed of heterogeneous components. Mixed continuous/discrete and hardware/software systems are used to illustrate these concepts. The benefit of reading this book is to arrive at a clear vision of the theory and practice of specification and validation of complex modern systems. Numerous examples give designers highly applicable solutions.