I love Harel statecharts. They are a useful formalism that maps easily to code for a wide range of practical solutions. The key innovation is embedded states.

I love Harel statecharts. They are a useful formalism that maps easily to code for a wide range of practical solutions. The key innovation is embedded states. That said, the formalism does not say much about error handling. This is where state machines can get really hairy, in much the same way that throw/catch gets nasty in any non-trivial system.