That is one of the early papers by David Harel which divulgated statecharts among the scientific community. Note that since then, there has been a number of criticisms made about the original statecharts (namely the absence of precise semantics, and the concurrency model) and a number of variants have since seen the day. What seems to have remained in all variants is the concept of hierarchy. In the Kingly state machine library (https://github.com/brucou/kingly), I only use hierarchy and discard broadcast and concurrency. The latter two can be added at will according to the problem at hand.