Based on a graduate course taught by the author, this book provides an in-depth understanding of the expressive power of various models of system behavior. The text details two fundamental types of requirements specification models: those that describe structure and those that describe behavior. Chapters emphasizing structure focus on entity/relation models, dataflow diagrams, hierarchy charts, class diagrams, and object diagrams as well as the interfaces among them. Sections highlighting behavior address decision tables, finite state machines, StateCharts, and Petri Nets. The capabilities and limitations of each model are also discussed. Practical examples and exercises complete the coverage.