Developing the UML-B Modelling Tools.

UML-B is a UML-like diagrammatic front end for the Event-B formal modelling language. We have been developing UML-B for over 20 years and it has gone through several iterations, each with significant changes of approach. The first version was an adaptation of a UML tool, the second generated a complete Event-B project, the third contributed parts of an Event-B model, and the fourth (currently under development) provides a human usable text persistence. Here we outline the reasons for these different developments and summarise the lessons learnt.