On the central role of action in JSD

In this paper, I survey recent developments in the Jackson System Development notion of `action´. Some polymorphic extensions to the notion are also examined. I demonstrate the importance of the notion of action in JSD and also bring together and document some of the more recent developments in this area. There are certainly implementation costs involved with such techniques, however the price is well worth paying, both for the increased modelling power required by the real-world applications of today and for the perhaps unreal-world applications of tomorrow