Posting this after a hiatus of more than two years. Have been studying Labelled Transition Systems which is the work of Milner's students and associates. More recently  the work of Paulo Tabuada on labelled transition systems with output. As noted in this blog earlier this model generalizes the models of Knuth, Dijkstra, and Chandy and Misra. A good candidate to explore in the study of formal methods in computer science and software engineering.